Just looking at my sandblasted M - I cannot imagine any particles flying off from it. No. Not at all.
Corundum ( a type of alumina ) or glass beads were most probably used for the sandblasting of the M.
Probably the latter,as corundum tends to remove lots of material and gives a more rough finish.
While glass beads ,as finer grit and softer material,give that awesome matt gray finish.
The particles of both sandblasting media will not stick /bond/adhere to SS316L.
With aluminium and titanium that could have been an issue (due to their galling when under friction ),
but is not an issue with most steels .
Futrthermore ,even if it was an issue the amount of sandblasting media particles ,
that could be possibly inhaled ,has almost null health impact and poses no health risk.
Cheers.