That photo is almost a duplicate of a raceway we worked on this year. My tech did clean it out, and we charged extra for that. He also filled a cardboard box with crap and showed it to the sign owner so the owmer could understand what was involved. Needless to say, that bill was paid in three days.
We have a theater marquee that had pigeon problems, and one of the maintenance guys bright idea was to string netting behind the sign and attached to the building to keep the pigeons out. Problem was, it quickly developed a hole and the pigeons got in, but could not get out. Several dead pigeons later... a hawk got a leg tangled in it. He got out, then they finally took the net down.
Good times...