Use TXDworkshop, download it from gtagaragehttp://www.gtagarage.com/mods/show.php?id=8320
Use 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