I’ve had some luck curving reproduction porcelain signs. I heat them up to 180f and then place a 2x4 of either side and then slowly apply pressure to the middle.I usually re heat them about three times before you get enough of a curve. I’ve never tried with an original sign so I can’t say if that will hold up.
You can do it with tie down straps, have done it many times. If I get out into the shop tomorrow I’ll take a couple of pics. Don’t like the large reproduction ones they don’t fit that well.
