We got the upstairs bathroom finished, and are working on the kitchen. I have an old farmhouse sink - the kind that sat on top of a metal cabinet, I think. Single basin, double drainboards. 60" long, 22" front to back; basin is 21" wide x 17" front to back x 6" deep; 10" high backsplash with holes for a wall-mount bridge faucet (8" center). I cannot remember how to post pictures on here - I'll get a link to my photobucket account up as soon as I get more kitchen pictures posted.

My question - there are markings on the bottom of the sink, similar to cast markings on an engine block. I haven't had any luck googling identification information. I don't know that it's important, I'm just curious. Anyway - the markings.
There's a large diamond shape that encompasses a capital "i" (sorry, the lower case L and capital i look the same to me); a large 3, the numbers 5203, and what appears to be a date - 3 28 (or 23) 30 (or 38). I tried to take a rub of them, like you would with a grave marker or engine block, and that's the best I can decipher them. I'm not sure if they're cast into the sink, or if they were attached later - on the '5203' and the date, there appear to be rivets holding plates, but not on the diamond or the large 3. I wish I could take and post a picture, but I tried and it came out awful

Any ideas? or can someone direct me to a place to find information? Like I said, it's mere curiosity.
About the house: built in the 1870s sometime, it's nothing spectacular as far as old houses go (not Victorian, or Craftsman, or Four Square, that I know of), just an old house on land that used to have apple orchards. I like the character of the house, but am not trying to do anything spectacularly authentic with it. Wood floors - downstairs except the kitchen are 3 1/2" oak; stairs are hand scraped oak; upstairs is 3 1/2" red pine; kitchen is 1 1/2" maple. Most of the walls are plaster over some type of fire board, reinforced with wire mesh. Upstairs bath was remodeled completely last year - it now has porcelain tile floor and a shower in addition to the vanity/sink and toilet. Kitchen is in the works - custom cherry cabinets, refinished maple floor (the linoleum was beyond hideous, and there were two layers), stainless appliances, satin nickel hardware and fixtures, including the aforementioned bridge faucet, granite countertops, stone/metal/glass mosaic tile backsplash and a tin ceiling. Downstairs bath is next, I think

Thanks in advance for help on the sink ID!