Wrong signup form code - the form does not exists

I see this in my logs often which leads me to believe that I have, over the years, created links to sign up forms that are now invalid. When I drill down to try to find out what link the log entry refers to it is not mentioned in the details.

If there are links people are using to get to my sign up pages that are no longer valid, what would be the best way to find out what link was used? What link did they actually click?

Thanks.

Which logs, aMember or server?

Yes, sorry I was not specific. It is the aMember error log. Here is a snapshot. The URL gets truncated so I am not sure what URL was requested.