If you mean getting the F.8879 signed so that you can e-file it for your client, you can use e-Signature if you subscribed to it.  A copy of the return with watermark will be sent to your client for review along with F.8879.

If you don't use e-Signature, you can use Intuit Link or your own secure client portal to share it with your client and have your client return a copy of the F.8879 signed in wet ink.

Otherwise, you can email a copies of these to your client but make sure you protect them with a secure password.  Your client should do the same when the signed F.8879 is returned to you via email.