Hampus Sjöberg has set up a site (https://taproot.watch/) with a graphic for which blocks have signaled for Taproot activation and a breakdown by mining pools. It was announced here on Twitter.
AJ Towns stated on Mastodon that once signaling starts the Bitcoin Core RPC getblockchaininfo will report the number of signaling blocks in the current period.
David Harding added on Mastodon:
If you want to implement checking yourself, you can use the versionhex in either debug.log or the results of
getblock. Taproot is using bit 2. See the versionbits FAQ for details about bits:
pox also wrote an awk script:
gawk -F'[= ]' '/UpdateTip/ { print("block="$7" taproot="and($9,2)) }' <~/.bitcoin/debug.log
If you are interested in which mining pools have already indicated that they will be signaling readiness for Taproot activation see taprootactivation.com.
Update on June 14th 2021: Taproot activation has now locked in and Taproot rules should now be enforced in November 2021. To verify this on your node use this script provided by emzy on IRC:
bitcoin-cli getblockchaininfo | jq '.softforks | .taproot
which should result in:
"status": "locked_in"