ATL Controller described a runway incursion that caused a very late Air Carrier go around on Runway 26R; the reporter indicated improved signage near the subject FBO may prevent future problems.

Narrative

While working Local 1; arrival Runway 26R. I had cleared a Heavy to land. There was a general aviation aircraft taxiing out to hold short of Runway 26R at Taxiway Dixie. The Heavy was already past the landing threshold almost to where his main gear was touching down. I saw the general aviation aircraft continue across the hold lines for Runway 26R. I sent the Heavy around not knowing if would be able to do it; or if he was committed to land. The Heavy was able to go around. The general aviation aircraft had stopped with his nose right on the runway edge line. His entire aircraft was past the hold bars. Recommendation; this has happened before at this intersection. The problem is when aircraft come out of the FBO to hold short of Runway 26R/8; and aren't familiar; as soon as they exit the ramp onto Taxiway Alpha they are at the intersection of Runway 26R and Taxiway Dixie. The only thing I can think of to help prevent this is to add more warning signs. Move the exit taxiway out of the FBO. There are two ways in and out of FBO but we can't control which way they come out.