Use TXDworkshop, download it from gtagarage
http://www.gtagarage.com/mods/show.php?id=8320Use paint to resize, make the text fill the image (remove the blank spaces).
Extract streak.txd and open it with TXDworkshop, the first two images are the logos
so replace them with your image using
import button. Once done
go to
Properties and uncheck
Alpha is used on both images.
Then save and you can install it.
For train cars the file is called streakc.txd