Section 174.15 - Validation stickers(a) If a State issues validation stickers, its numbering system must contain the requirements that stickers must be displayed within 6 inches of the number and the stickers must meet the requirements in paragraphs (b) and (c) of this section.(b) Validation stickers must be approximately 3 inches square.(c) The year in which each validation sticker expires must be indicated by the colors, blue, international orange, green, and red, in rotation beginning with blue for stickers that expire in 1973.