Reality Askew

Was listening to an audio book on the way to work the other day dealing with a fictional military battle and it got me to thinking.  In the book there is a great deal of vehicles (Tanks, Infantry Fighting Vehicles, Artillery, etc.) that are being attacked primarily by aircraft.  However a lot of the attacks rely on the attacking aircraft keeping eyes on the target.  So my thought was what if you could develop a laser type weapon that would somehow paint a target in such a way that it would leave a radiating patch on it that a weapon system could home in on.  By radiating patch, I mean, for instance, the top of a tank would get zapped by this laser type device (maybe even from space?) and that would leave a round area on the top of the tank that a weapon system could lock on to.  In my scenario the laser device “paints” the target once and then moves on to the next one, leaving behind this area that sort of glows or radiates.  Unlike current targeting system, the laser wouldn’t have to stay on the target for it to be illuminated.  I know that’s sort of rambling but I want to be clear on how I envision this working.  Maybe you could somehow project radioactive isotopes down a laser beam and have them splatter on a target?