Most of the signature campaigns give the same amount of stakes to Jr.Members and members. I think it is not fair, especially now, when Jr. cannot have clickable links in their signatures
This is not correct. Member ranks gets almost double of what Jr Members are getting. Some examples:
https://bitcointalk.org/index.php?topic=3036499.0Rates:
Jr member - .00075/week
Member - .0015/week
Jr Member with at least 1 merit - .00125/week
Member with at least 2 merit - .0025/week
You can observe similar trend in other campaigns allowing Jr members. These campaigns are allowing Jr Members even though there signatures are not clickable. However, number of such campaigns is very less. Regarding OP's comment that this is not justified, I guess ranking up to member level is not hard if someone is active and constructive with his posts here.