This question already has an answer here:
In User signing up to many stackexchange sites and offering the association bonus as a bounty a case is being discussed about a user that got 200 reputation in one of the Stack Exchange sites and hence he gets the association bonus whenever they sign up in a new one. Then, they have a reputation of 101 points and they offer a 100 bounty to some question.
As of writing, this has been done in over 100 sites, and in most of them they just joined today and their first action was offering such bounty. Sometimes, also a comment was written down. Nothing else in most of the cases.
A bounty has a big impact: it attracts a lot of traffic, which in a sense is "taken" from others in the front page. Thus, placing one is a big action towards the site.
While the purpose of these bounties can be OK and offered to questions that are worthy, this very specific case has showed that the system can be a bit perverted and a non-experienced user can have a big impact on a site (or multiple ones).
Currently, the privilege to set bounties is set to 75 reputation points in all sites (beta and graduated). This means that you have this privilege if you ever when signing up in a site if you ever got 200 in any other site. That is, if you are granted the association bonus.
For this, I suggest raising the reputation for the bounty privilege to something that involves having been somehow active in the site, for example 125, to the same level of the privilege of voting down.