Sadly, on Android devices, nothing seem to work. 

The Gmail app on Android does not read the signature from G Suite so it has to be edited yourself if you wish to attach your signature to your outgoing email messages. 
Thankfully, there is a solution, even if it may seem a bit severe: Switch to iPhone! Or ask Google to provide better support for signatures in Gmail on Android devices. 

We have a feeling that for you Android users out there, this will be the preferred means of protest!

Google has recorded this feature request