Barcodes on Tube Platforms - Anyone know what they are?

Does anyone have any idea what these things that look like barcodes are?  I spotted them for the first time a couple of days ago at Liverpool Street London Underground station, and am pretty positive I've not seen them anywhere else.



They might not even be bar codes but certainly look like they could be measuring something or would possibly activate a sensor when a train passed. I really have no idea, but am certainly curious to find out if anyone knows.



Here's one closer up which may help with identification. Thanks.

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