The signature solution you are describing sounds like a "click-through" signature solution. Here are some links to info that discuss this type of solution, hopefully you find the information useful...
By the way, you could achieve what you would like to do using LiveCycle.
Actually, that is what we're heading towards... a LiveCycle solution.
With an eForm processed via LiveCycle, can someone sign-off a part of an eForm quickly and easily... using only his/her login credentials?
Or does s/he still need a digicert?
LiveCycle and Acrobat\Reader support the creation and validation of "Digital Signatures" using digital certificates. A PDF form can contain one or more signature fields, so one or more people can sign the same form. Whan a user signs the form they will require a digital certificate.
Digital Signatures provide a method of validating authenticity (the form was signed by the intended party) and data integrity (the data has not changed, or the changes that occurred were allows by the document author)
If you do not want or require the level of "protection" that digital signatures provides, thenm you may want to design you solution to use something like the "click-through" signature, which is NOT a "digital signature", but it can be considered as a type of "electronic signature"
There are many type of "electronic signatures", a "digital signature" is one type of electronic signature.
Hope this helps