Either pissed people having a laugh moving the sign around, or it was people who objected to the LTN moving them. I don't think anyone ever got fined at the School Street LTN I linked to, there were no cameras and very little official enforcement (only a bunch of volunteers that encouraged motorists to take the obvious alternative route).
The LTN signs are always badly put up, the ones near the school street near us are the same:
https://maps.app.goo.gl/fCuuRkg1JCaGYxGNA
Either pissed people having a laugh moving the sign around, or it was people who objected to the LTN moving them. I don't think anyone ever got fined at the School Street LTN I linked to, there were no cameras and very little official enforcement (only a bunch of volunteers that encouraged motorists to take the obvious alternative route).