What app version are you on? I'm pretty sure we have Temp Sig Authority in GSM as well. check GSM>>Temp Sig Authority.
Although in GSM, user need to grant a role [TSA_ADMIN] to enable create/modify TSA. Hope this will solve your problem.
Jessie, what David is talking about is in NPD the TSA allows the disignated user to do many things for the original user. They can sign off on sig requests, edit their projects if they are leaders, sign off stages if they are gatekeepers, edit owned activities, etc. It basically allows the TSA user to do anything the original user can do.
However in GSM TSAs are only for Signature Requests. Our spoiled NPD users want the same functionality in GSM. :-)