I signed in to "Fill & Sign" mobile app and created a new signature using a stylus and saved it. I then made sure I was signed in with Adobe ID on desktop Adobe Acrobat DC. After opening a new PDF to test my signature, I cannot find an option to use the signature I created in the mobile app. The steps I have found thru Adobe's website just say that the signature will be synced across all devices when signed in.
We are sorry for the inconvinence caused to you. Could you please confirm the following :
Go to the settings option in the Fill and Sign mobile app and check whether the Store Profile Online has been enabled or not?
If not, then please enable it and try again. It should be enabled to allow syncing of data across devices.
Let us know how it goes.