In New York City, when they need to do construction/repair/whatever to the pipes/wires/whatever underneath the street, SOP is as follows: 1) dig a big hole in the middle of the street; 2) slap a very thick metal plate over it; 3) leave as is for 3-6 months; 4) come back and do the actual work; 5) replace the plate over the hole; 6) leave as is for 3-6 months; 7) take away the plate and fill in the hole.
These plates are massive, 2 inch thick iron (?), which can support the weight of traffic. They are apparently cut to size as needed (which can be 20’ x 20’ or more, HUGE slabs of metal). When I say “cut to size”, I mean that there are obvious cutting torch marks around the edge; this thing wasn’t finished to it’s present size in a mill.
There are usually also what appears to be a set of initials burned (welded?) in the center of the plate. I have heard from several people that these are the initials of the guy who cut it, such that they would know who to hold responsible if the plate failed.
OK – what are they really? Sometimes it’s just two letters, sometimes contains a numeral. Likewise, the explanation seems like an urban legend. I mean, I’ve seen fully loaded gravel trucks sit on these things (not just roll over them) without a discernable ‘bend’ in the plate. My guess is that they could get away with using a thinner plate, but have over-designed due to the possible consequences (i.e. vehicles falling in the hole). I can not fathom a scenario where one of these would buckle and/or break, and likewise the guy who cut the 40’ x 20’ slab in half wouldn’t be responsible for the tensile(?) strength of the resultant two slabs (if it came from the mill flawed, why would the “cutter” be held responsible?).
So… what significance are the letters burned into the middle of these plates?