are signs and posters allowed at concerts (specifically the Taylor Swift concert)? And on the floor especially?

Or you can ask @taylornation on twitter.

I can't help you with that

When we went to see the game they didn't let us bring in posters.

I saw Coldplay there twice and there were lots of signs everywhere, including the floor. I think there may be a size limit, which is listed on the stadium's website.I have tons of photos posted from there. You can probably see them by clicking on my name or the 3 dots on the right.

I think they usually are allowed. Call the venue and ask

In others concerts sings and posters are allowed but I don't know about Taylor's concert.