The unique screen model number can be found on a manufacturer's sticker on the back of the screen. Typical sticker will have a barcode and an alphanumeric model which usually in some way includes the size of the screen (see some examples below).
Here's a few examples of typical LCD screen model numbers:  B089AW01, CLAA141XG01, HSD150PX17, LP141WX1, LTN140AT02, N141X2,QD15TL09, UB133X01.