And even if they did...most of the time their opinion would be "yeah, looks OK". You'd like that to just be stage 1 and call for further scrutiny if it turns out it would affect the result - but you can't, if you keep the evidence longer to revisit it during a recount, you lose the secrecy of the ballot.
You can do it the other way around. If the signature seems fishy, you set it aside unopened, and only do further validation before opening it if the election is close enough for it to matter.
For example, in an election with 100 votes cast. If 10 signatures are suspicious, you only do extended validation and open them if the election was won by a margin smaller than 10.
I’m confused.. do you think it’s likely that someone forges the signature of a person they’ve never met within a believable margin of error? Seems the burden of proof is on the people claiming that happens a lot