For this step, you will need a bunch of 50mm Round RFID tags that match the RFID card reader (Parallax part 28142): these are EM4100 family tags that have a 125 kHz activating frequency. You will also need a color printer (inkjet or laser), self adhesive labels suitable for use in a printer, scissors, and of course artwork.
Find artwork that you want to use to represent the web site you want to associate with tag.
Using your favorite software, print the artwork onto the labels (I used Avery labels and their online label printing software.)
Cut out the labels and stick them on the tags as shown in the second photo. You can put the sticker on either side of the tag.
In a subsequent step, the process for updating the program to recognize the tag will be described.