Who can sign an aia for a subcontractor office

Yes, if you have authority from your company to do so.

The instructions for the AIA documents state that the contracts should be signed by the company's authorized representative, with their title noted, and corporate/company authorization attached. Technically, you cannot act as an agent (authorized representative) for a business entity without express (usually written) authority by the entity. However, if the person who gets your signature has been given reason to believe that you are acting on behalf of the entity, then they are entitled to rely upon it. For your own protection, you should get written authority from your company even if no one requests it.

If you have an attorney that your business uses, they can draft an authorization. It could be limited to lien releases and payment requests, unless you have a larger role in the company.