So we're planning on having this "event" in June, where as many high rep people as possible fling as much reputation around in bounties as possible. The idea being 1. Why not? and 2. To attract more users.
In aid of the second objective, we need to make people outside of checking TSE every day aware that the event is even happening. Obvious candidates for this are existing Stack Exchange users.
Non-beta Stack Exchange sites (except maybe SO?) have a thread in their "meta" area, called "Community Promotion Ads - 2016" where users of that site can post images that will be shown in the sidebar. Here's the Travel one.
What could be done as a start for promotion is taking the image we already have to promote the event within TSE, and spread it elsewhere. As I can imagine (quite reasonably) other communities feeling annoyed or spammed by simple "drive by" posts, this should ideally be done by people who are established memebers of the community on that site (at least having a reasonable reputation count) and who personally feel that there may be some genuine interest from that site. Obvious candidate (to me) would be Aviation and Bicycles. Academia and The Workplace might also make sense.
The post in the ads promotion should look something like this:
[![Travel.SE Great 5 Year Anniversary Bounty Bonanza][1]][2]
[1]: https://i.sstatic.net/OIr0S.jpg
[2]: http://travel.stackexchange.com
Please post an answer here if you have submitted the image to another Stack Exchange network site. (Although others please note - this isn't a call to "brigade" upvote it)