Hi Jaycee.
Whenever you open a bank account, take out a mortgage or do anything financially, you are required to provide a profe of id using a recognised, signed item.
This is usually driver's licence, passport or bank card. Usually when you apply for a loan then you have to provide these as proof of who you are and also as a control sample for your signature.
The lenders will have the original forms or at least copies of them, which can be compared with your driving licence and passport. If need be, these can be compared at a very detailed level and proven to be forged.
The weight used when doing letters in a signature, the angle at which letters are done, things like that.
This is the extremely detailed level of things but with my friend she had managed to really make a hash of the signature to the point where neither the loan form or the control (passport) looked the same.
Richyboy, I've just had a thought about you saying that she claims to be still living with you. Did you inform the council when she moved out, with regards to council tax?