WM/Sig is a simple macro virus which contains a macro called "signature". This virus is not widespread.
Sig activates by adding a single line saying "WIN" to the end of AUTOEXEC.BAT file.
[Katrin Tocheva, F-Secure]
Once detected, the F-Secure security product will automatically disinfect the suspect file by either deleting it or renaming it.
More information on scanning and removal options available in your F-Secure product can be found in the Help Center.
You may also refer to the Knowledge Base on the F-Secure Community site for more information.