That's why political parties were invented, so you don't need to create name recognition for every candidate.

Those signs aren't changing anyone's mind. But a party is something people can talk about and understand. It's unifying.

Giving a fuck means engaging with party politics and making it part of your day to day life (at least during election season).

Signs are the laziest and most inconsequential way of supporting a candidate. By far the best way is to convince everyone that you know in person to vote for a particular candidate.