Segregated Witness (SegWit), the Bitcoin protocol upgrade proposed by theBitcoin Core development team, was originally designed to activate via the Bitcoin Improvement Protocol 9 (BIP 9) standard, a hash-power signalling mechanism. This would allow the Bitcoin ecosystem to coordinate the upgrade relatively safely through miner readiness.
But with the SegWit proposal in particular, BIP 9 no longer serves just to signal readiness. Miners as well as users increasingly see BIP 9 as a sort of miner vote on the desirability of the protocol upgrade. And some miners even seem to utilize it as a negotiation chip for protocol development.