What are the most common barcodes used for key tags and gift cards?

The most common barcode is referred to as Code 39 or Code 3 of 9. Code 39 uses a combination of letters, numbers 0-9 and special characters ($, %, +). Typically cards and key tags are encoded with a random, 8-digit number. Code 128 and UPC A are other types of barcodes that can be found on cards and key tags.