This strikes me as unusual. What usually happens is the company writes a letter offering terms. Sometimes there is a space on the bottom for the employee to sign and return one copy.
When I've been issuing a letter CHANGING someone's terms, I write a phrase at the bottom 'I have read the above letter and accept the change in my terms of employment. Signed..... '. That covers my company.
I think (but I'm not sure either) that by issuing the letter, that is enough for an implied contract, as Clio suggests.
Is there at least a signature of an (authorised) person from within the company on it somewhere?