I am just curious what a phrase "e pluribus smart assimus" means.
This is dog Latin for "out of many come smartasses" (or "a smartass"). It's modelled off the phrase ē pluribus unum, "out of many [comes] one", which is printed on American currency, plus the fake Latin smart-assimus for "smartasses". The -us is typically a singular ending, but is also commonly used to create dog Latin in general.
As a side note, while "smart" of course isn't Latin, assimus is a real word: it's the first person plural present active subjunctive of adsum/assum, "to be present". So assimus means "let's go be there!" But that's certainly not what the author of this phrase intended.
In the "National Sarcasm Society" plate, it's written: Like we need your support
below that, the complement:
E pluribus Smart Assimus
among so many smartasses.