Sign — of possible decay? (6)

I believe the answer is:

plaque

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'sign of possible decay?' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?

This is all the clue.

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(Other definitions for plaque that I've seen before include "Sticky deposit on teeth" , "Substance that forms on teeth encouraging bacteria" , "Film on tooth" , "Memorial slab" , "Memorial plate" .)

I've seen this clue in The Times.

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