How to check if 2 email fields have the same value entered during content creation?
Assuming this question is about D7, you could use the Rules module and create a (rather basic) rule like so:


Rules Event: Before saving content
Rules Conditions:


Content is of type "custom signup".
Entity has field (related to your 1st eMail field).
entity has field (related to your 2nd eMail field).
Data comparison: the value of the 1st eMail field is NOT equal to the value of the 2nd eMail field.

Rules Action: Show a message on the site (of type "error").