That page doesn’t mention the license under which the logo is released. Thankfully enough, this discussion was resolved some time ago when we wanted to use the new logo on the wikipedia page: File:Jmonkey-logo-head-tilted.png - Wikimedia Commons
The license is “CC BY SA 4.0”:
https://creativecommons.org/licenses/by-sa/4.0/deed.en
However once again there’s confusion, because @erlend_sh did not clarify who is the entity to be attributed as required by the license.
Based on the metadata on the wikipedia page, Erlend himself is the author and thus must be credited as follows:
jMonkeyEngine Logo (c) by Erlend Sogge Heggen
jMonkeyEngine Logo is licensed under a
Creative Commons Attribution-ShareAlike 4.0 International License.
You should have received a copy of the license along with this
work. If not, see https://creativecommons.org/licenses/by-sa/4.0/.
I will wait for his clarification and then update the wiki page with the license information.