I am not aware of any alerting system to detect active censorship.
@0xB10C runs miningpool-observer that's designed to aid detection of censorship. When you click on mined blocks in Mempool.Space, it shows actual vs expected blocks too.

I'm looking forward to read more of these. I found Cryptoeconomics a bit of a pedantic bore but valuable in aggregate.
Thanks for mentioning this tool. It would be ideal if it raises loud alarm when a transaction is being persistently excluded from fresh blocks.
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There's also an RSS feed with showing OFAC sanctioned transactions here: https://miningpool.observer/template-and-block/sanctioned-feed.xml (currently empty because I switched to a new database). In the past it alerted me about F2Pool censoring OFAC sanctioned transactions. See https://b10c.me/observations/08-missing-sanctioned-transactions/
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