How do we identify an Observer , Signer become not active

After https://gitlab.com/thorchain/bepswap/statechain/merge_requests/142 First of all, statechain will mark an observe to active if it see the observer observe transactions on binance chain , and forward those transactions to statechain. Secondly , nextpool memo will prove the signer is active.

With that , how can we easily detect an observer is not active? , how can we detect that a signer is not active? @jpthor @cbarraford can you please share what you think here?