There can be signature of Receiver and Sender both on proposal.
You(Sender) can essentially save your signature in Profile section.
Get to know IP address of receiver when he/she opens/signs the proposal through audit trail.
Once you have sent the proposal to client, if you want to update it then signatures will be removed if any on proposal so it abides by the laws.
Click on proposal module -> There is block as signature. On clicking it signature blocks for reciever and sender will be inserted.
To save the signature in profile section, Settings-> Profile -> Add signature.