I liked this post and will find use for it in the work I do.
In my experience, repeating a name out loud, or doing some other visible memory trick. Is a good way to signal trying to remember names. Then, if later you forget you are more easily forgiven.
A useful person to have at any meetup is a greeter who says hello to arrivals and engages them in a minute or two of conversation. This is especially useful for first time attendees, who might otherwise mill around unsure what to do or how to introduce themselves. It's even better if the greeter makes an effort to remember names or to direct newcomers into conversations with others. The summary of this post is that if you want to make people feel welcome, I recommend having someone intentionally filling the greeter role.
You have now read the basic point of this post. If you want to read on, cool, lets talk about implementation details for a bit.
Approaching a small crowd of people talking to one another, it isn't always clear how to introduce yourself and interject into their conversation. It can feel rude! How do you even know if this is the meetup you're looking for? If someone looks at you and says "Hello! Are you here for the rationalist meetup?" then that's an easy question to answer! If they follow up with "I'm glad you found us! I'm Bob, what's your name? What got you interested in rationality?" then now there's a conversation.
It feels nice to be somewhere everybody knows your name and they're always glad you came. That place can be your local rationality meetup! "A place where everyone recognizes everyone else by sight" isn't a bad working definition of a community really. It doesn't fit every group but it's a nice thing to aim at. If your community is online in say, a Discord, consider how many regulars you can identify by chat icon.
Many of us don't feel confident in our ability to remember names or recognize faces. The greeter doesn't actually have to remember names or recognize faces. That short dialogue example above? That first line works just fine even if you can't recognize people. If they respond with a variation on "Yeah, how've you been Bob?" then you know you have a repeat attendee. People give you a lot of leeway to forget names, especially in loose groups with irregular attendance.
That said, remembering names and faces is a skill you can get better at. Seeing everyone's face in association with their name is the obvious easiest way to get better at it. I made large improvements in my ability to remember names by paying attention, which was obvious in hindsight. I remember zero of the bricklaying patterns on the street, but when I was taking a layout class I remembered some stores by what font they used on the sign. Suggestions specific for getting better at names are here.
You don't actually have to be appointed The Greeter. If you attend a meetup where nobody is doing this, you can just start. It doesn't need to be official. You can even have multiple people attempting to say hi to every person who shows up. Vary the script; there's no point saying "Are you here for the rationalist meetup" if they've already started talking to people, but in a general socialization meetup it's fine to say hello to each person in a small conversation.
Saying hello to each arrival is a sufficient Minimum Viable Greeter. You can do more though! If there's something you want to tell everyone at the meetup a greeter can do this on a rolling basis. At ACX Everywhere, I often have a roll of nametags and a mailing list signup sheet. Saying hello combines very well with offering them a nametag and a chance to get emailed about future events. If you just want a count of how many attendees you had, the greeter can just keep a count (in their head or on a piece of paper) of how many people they introduced themselves to.
I like doing what I call Air Traffic Control for meetups. Part of the questions I ask people as I say hello is what they're interested in. When I'm paying attention, I have enough working memory to keep a small list of who is interested in what. "Nice to meet you Carla! I don't know much about neuroscience but I was just talking to Adam a few minutes ago, he's over there in the green jacket and he's doing a masters degree in it. Here, let me introduce you!" I find it a fun little sorting puzzle.
You can also apply this when people are leaving the meetup. "Nice to see you Dean, I hope to see you next time!" Repeating their name helps you remember it, and it ties into the feeling of being known and part of the community.
If your group uses nametags, the person holding the nametags and writing implement is a good greeter. If you are the organizer, people may assume you are doing a greeter role; I've heard variations on "Hey, are you Scott? I'm Harold, I heard about this on facebook. Thanks for running this!" You may as well lean into it.
This default greeter role does mean if the organizer is going to be busy setting up AV cables or preparing food or something like that, greeters can be good for giving them space to focus. "Hi, I'm Scott, are you here for the meetup? Cool, nice to meet you Harold! Alice is the organizer over there but she's busy setting up the projector at the moment, tell me how you found the group?"
If you are an organizer who dislikes talking to people, consider asking one of your more outgoing regulars to do this.
Remember the goal is brief conversation. Ideally you want to naturally wind up each conversation just as a new person arrives. "Someone new just arrived and is looking lost, but have fun at the meetup!" is a good quick social disengage.
Repeat their name after they tell it to you. This is not as awkward as it sounds. "Nice to meet you Elly! Elly. Elly. Elly. Cool, just trying to keep everyone's name straight." It is a little awkward, so if you can confidently remember names without doing this that's better. In my experience, people are mostly pleased that I was making an effort so I sometimes do it even if I'm 80% sure I'll remember their name anyway. In the last five years of actively doing this, nobody has said they were annoyed at me for writing their name down on an index card along with a short description.