I have one Nikon lens with a really nice JCII sticker - so I left it on. If the sticker is ratty, it comes off. Wipe with a LITTLE Goo-Gone to remove the adhesive.
For those that don't know, JCII stood for Japan Camera Inspection Institute. It was to convince people that the photo equipment met certain quality standards, as some cheaper Japanese cameras were pretty bad. It might be sort of compared to our UL (Underwriters Laborities) or ASTM (American Society for Testing and Materials) which are industry self-policing groups to maintain quality.
I think JCII did a good job, but ourgrew it's need and got merged into other quality organizations.