I believe that it's actually "Union Switch & Signal."
They manufactured M1911 pistols, licensed by Colt's, during World War 2.

Look at or just under the top of the pistol's right-hand grip panel for "U S & S C O," or on the left side of the slide.
If it's in really good condition, your pistol could be worth as much as $4,000.00 (or as little as $850.00, of it's an arsenal-reworked gun).

If it was made in 1953 it was not a US&S, or a Government issue pistol the last M911A1s for the US Government were made in 1945.

It is possible there is an error, either by Colt or the OP.

Union Switch & Signal made the following pistols. I'll double check again when I get home from my source in print.

1943

*1041405

1096404

Union Switch & Signal

55,000

What we really need are picures of both sides of the gun, as well as the top of the slide.

IF it's an original US&S, it's about as priceless as you can get regarding M1911A1 pistols with the exception of a Singer (only 500 made)

Find anything out?Being an heirloom trumps everything but it would be nice to find out exactly what it is and value.Go to Proofhouse and check the serial number with their records in case Colt somehow oopsed.If it is a US&S,it's possible it's still original,but if it's really seen alot of war use I doubt it.The '53 has me wondering if it's a rebuild or a communication mistake as VA and Steve mentioned.

Forgot,I think Proofhouse also has catagories for hammers,safeties,most parts in general.They have pictures of the variation of the parts throughout production so you can tell fairly easily if a slidestop or safety belongs in that pistol or was put in during a repair or rebuild.

This past weekend I got to shoot my wife's deceased grandfather's 1940s issued Colt M1911A1, now in the possession of her uncle. I guess after 12 years of marriage and three kids, I am officially a member of the family. And as to the gun...WOW!

If her Uncle shoots it often,tell him run ball,or standard loads or lighter through it if it's in nice original shape.Heat treating of the slides were being done but it wasn't to today's standard.The gun may shot forever,but if you break something on a nice old specimen it can really kill monetary value.I'm all for heirlooms because I have some,but don't screw them up for a hand-down in the family or quick real cash if you need it in an emergency.