Is there a limit to the amount of area that can be wiped in a series of complex actions? Is the astral signature where a spell was cast distinct from that of where it took effect? If I cast a fireball here that goes off over there, is that one wipe or two wipes? What if a sustained darkness spell was moved over a large area? Is that entire blob one astral signature?

I just treat each spell as a single signature. Doesn't matter whether is is AoE or single target. Just makes it easier. Generally the signature appears where the spell was cast (around the caster).

Yeah, who knows if its rules-intended, but we would go 1 spell = 1 signature, even if its kinda big effect. So the kabloooooie of that super hellball explosion may have leveled the food court, but if you spend the time to erase the signature, it follows rules as normal. I'd also go with 'spell signature is located where caster was."

In the description of Astral Signature on page 312 SR5:


In SR4 it was not explicitly defined, that the signature is at the place of casting and at the place of effect.

Other than that it is only written, that the signature is wiped out.
Depending on the GMs interpretation that could mean:
If I can see a part of the signature, I can wipe out the signature (all of it). Easy.
or
if I can only see a part of the signature, I can only wipe out this part. In this case wiping out the signature of a fireball can take a long time. You would probably first go to the center of the fireball (somewhat difficult if the environment is still burning around this place) so that you could do a 360 degree turn to see all places where fireball affected the room. And you would have to look up and down from the center of the fireball.
With that you should probably have seen all places with signature.
Somewhat complicated in case of indirect spells area effects.