Well.... Yes, that limit seems to be 512

However.... I tried to change this number in the file "misc.c" on line 26 and "oldloader.c" on line 393... I changed it to 1024 and compiled the game again.... but..... now, it looks, I can make more and more signs... But if I try to change name of a road vehicle/train/station, the game crashes... Does anybody know, if it is possible to make this limit higher for rvs/trains/stations higher too ? In which file ?
Note : I can rename rvs/trains/stations....but just only in the limit 512.... My game is somewhere very close to this limit... so when I rename something as soon as I start the game, it is OK.... but if I create about 20 signs (I am sure, it exceeds the 512 limit), I can't rename rvs/trains/stations then...