On the room editor just press 'Animating Backgrounds' to animate the whole bg, to animate it as an object you could just cut out the sign when it's on and save that as a bitmap on it's own, then import it as a sprite, make a new object in the room, set it's image to the 'sign on' sprite then position it correctly. In your script you'd have to script it becoming visible then dissappearing repeatedly.. a way you could do this is something like this in your repeatedly excecute interaction:
signcounter++;
if(signcounter==20){ObjectOff(Numberoftheobject);}
if(signcounter==40){ObjectOn(Numberoftheobject); signcounter=0)}
and in your room script near the top, outside any functions put the line
Int signcounter;
That would make the sign turn off after 20 game cycles and on after another 20 repeatedly, (there are usully 40 cycles per second)
If that is too hard then you could just animate the background, it basically just means the filesize will be bigger
