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]
Depending on the settings of your F-Secure security product, it will either automatically delete, quarantine or rename the suspect file, or ask you for a desired action.
More information on the 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.