Had a couple of prewar Railroad Crossing signs that were bent and needed to be straightened.
I m sure some of you also faced the same problem. I did not want to use pliers as this still would have made the sign not completely flat and could have scuffed the sign.
Came up with this idea, using two pieces of wood and cutting two slots in one of the wood sides.
These slots are to place the two mounting tabs of the sign in (make sure the two slots are deep enough).
Place signs mounting tabs into the slots and place the sign against another piece of wood or any hard flat clean surface and tap with a hammer. After each tap you can adjust the placement of wood to the sign. For larger crossing signs I would just use thick wood lie a 5/4 of 2 inch thick. I used a band saw to cut the slots in. if you do not have a band saw you can use a hack saw as long as you have square cuts.
The results will be a lot better than what you had before.