At a minimum, speak positively of unions to those around you and, if possible, educate those that don't know. So many people think unions are a bad thing from the historical propaganda.

fun thing, your workplace doesn't have to be unionized for you to be part of a union, it just helps if most of it is. i know a dental office that is represented by the teamsters.

Union Now is worth supporting

join tech workers coalition or no tech for apartheid. There's a lot of behind the scene work they do at a global level that doesn't require any exposure

Sneak a few fliers up around the office? Careful how you print them though, cause they'll probably print with tiny yellow fingerprints hiding highly identifying information