If you want to express support for someone with your vote, it should be “por.” That is the preposition that goes with the verb “votar.”

“Para” doesn’t make sense in that context, unless you work for him, that is the preposition that goes with “trabajar.” ... [But] actually the best option would have been “con,” that expresses general support. “Latinos con Trump.” But I don’t think they will print many of those signs.