Is Possible to Registrar a MAC Address in a VPN

Hi Gurus, I have a question:
I have a connection VPN to my Branch Office, but some day the Network administrator send an e-mail and he tell me that I must be disconnected the VPN. But In that moment I don't use the VPN, Someone was coneccted to the VPN I think.
The Question is:
I want to know if exist a System or tecnology that when you access a VPN, the firewall (or equipment that manage the VPN) register the MAC address of the Station/PC that use the VPN?
For example If someone know my user/pass of my VPN can do anything in my branch Office, and the Network Administrator would think that I do it. When I'm not the person that use the VPN.
Thantk gurus for your suggestions or advice
Andres