SUMMARY
An option to disable spell checking in email signature

STEPS TO REPRODUCE
1. Enable the spell checker pop-up on email's dispatch.
2. Create an email signature with words that are not in the dictionary (like for example the name of your company, a postal address with a street or city name)
3. Send an email with that signature.

OBSERVED RESULT
The spell check will warn for all the non existing words, including those in the signature.

EXPECTED RESULT
The spell check would ignore the non existing words in the signature (or at least there an option somewhere to have this behaviour).