A "bump" (in the Guilds section of the forum) is a response to a thread for the sole purpose of raising its profile.
So, no: "bump", "up", ".", or anything else that adds no new meaning.
Are duplicate threads allowed?
No.
What can guilds do to raise their profile?
The Guild section of the forum is a unique part of the forum where you are allowed to post in a thread to raise the threads profile, as long as at the same time you say something meaningful.
For example: guild news, updates on how many players you are looking for, or updated recruitment posts, and things such as these. But no repeat postings. Do not repeat the same message over and over again.
Also, some guilds have a few different members come and post in the recruitment thread.