Recently came across this blog post on Language Log summarizing this recent paper by Laran et al. Super-short version: When people are aware that a slogan is trying to persuade them, reverse-priming effects in which they avoid doing as it suggests can be seen.  However, if their attention is drawn away from the fact that it is trying to persuade them, the usual priming effects are seen.

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The takeaway for advertisement seems to be, "Don't persuade, just strengthen salience of a brand or its desirable connotations." Tobacco advertisements seem to follow this rule, it's all happy faces or symbols of status and no content. Probably depends on how intrinsically persuasive the hypothetical arguments are though.