You have to edit your profile.
I did it on a pc, so not sure where to do it on taptalk
Sent from my VKY-L09 using Tapatalk
I think on TapaTalk these are the steps:
1. From the main App screen - select "Me"
2. Select "Settings"
3. Select "Signature"
4. Select the forum for which to set the signature (Ecigssa in this case)
5. Edit the default signature (in my case: Sent from my iPhone using TapaTalk)
I hope this is what you are looking for.