1970 Z28 VIN ON BLOCK

[StriperSS]

Isn't there a way of 'seeing' the numbers on a decked block by magnetic means. I heard this years ago and wonder if it's true or an urban myth. It seems to me that law enforcement agencies could pull up serial numbers from guns and blocks that had been filed or ground off.
The stamping disturbs the metal molecules in the areas around and under the actual stamp, so even though a layer of metal has been removed, the disturbed area still exists, and can be read with some means.
Any opinions or knowledge on this?