Where allyship can involve flagging support it usually involves something that puts your skin in the game.
Showing up to an allies-welcome LGBTQ meeting, for example, can help provide cover for queer people who are at the meeting. Wearing a flag pin to show support can draw the same hostility that we would get.
This is a complex topic, not always appropriate, and not one I want to get into except to point out: where aiming to provide cover, it's best done in coordination with the marginalized