I attended a presentation a while back by a guy who was working on thermal fingerprinting/watermarking for ASI[CP]s. It was targeted at design/soft-IP producers

I attended a presentation a while back by a guy who was working on thermal fingerprinting/watermarking for ASI[CP]s. It was targeted at design/soft-IP producers, to detect if a particular chip was using their SoC modules without a proper licence, by observing particular thermal signatures each IP block generated. The cool bit was how it integrated deeply into the actual block layout, to make it harder to remove. It wouldn't stop the problem of a malicious manufacturer with sufficient resources from adding nasty things, but it could probably raise the bar a bit.