Stickers have to come off the tanks at Visual Inspection time to see if there is underlying damage, why would you put a sticker on a tank that is that hard to remove?
Because the lettering is crystal clear and doesn’t require the reader to study the poor penmanship found with white paint marker on 2” wide black electrical tape. The decals also make the tanks super easy to distinguish from others from afar whether topside or UW and because the reflective qualities make it easy for your mates to identify you during low vis diving. The decals linked above are super durable and look good after hundreds of dives and getting jostled around in the back of trucks and in and out of fill stations. Lesser decals will deteriorate over a year of frequent diving.