As a user
when I login without signing up
I get a message that I don't understand or read

A friendly message should be displayed.
Notes:
A current trend, due to security, is to advise the user to reset their password, if they have an account, an email will be sent to reset. If they don't receive an email within XX minutes then sign up.
A feature could be to direct them to the registration page if an account is not found and give them an opportunity to sign up with the credentials they provided.
As a user
when I login without signing up
I get a message that I don't understand or read
A friendly message should be displayed.
Notes:
A current trend, due to security, is to advise the user to reset their password, if they have an account, an email will be sent to reset. If they don't receive an email within XX minutes then sign up.
A feature could be to direct them to the registration page if an account is not found and give them an opportunity to sign up with the credentials they provided.