Well, you should include the character limit on each rank so that they will know that some signature designs are not suitable for other ranks.
Thanks for letting me know. Post updated.
Anyway, in my point of view is that you are trying to help jr. members how to change/add signature which is for jr. member to be able to join sig campaign.
Yes mate. My main purpose was to attract JR.Members. Moreover, I think it will be also useful for those(Jr.+) who don't know about it. It may be that those who are new to the forum but have got a lot of merit in some of their posts and they have gone to high rank but are inexperienced about the signature campaign.