Hy Logo is TeXGyreBonum font with the two parentheses, and two copies
of the lambda character all flipped around and rotated!

Aside from the font design (which was not done by any Hy authors!) the
Hy logo is authored by Christopher Allan Webber in 2013 and released
into the public domain under CC0... see CC0_1.0.txt!

  To the extent possible under law, the author(s) have dedicated all
  copyright and related and neighboring rights to this logo to
  the public domain worldwide. This software is distributed without
  any warranty.

  You should have received a copy of the CC0 Public Domain
  Dedication along with this software. If not, see
  <http://creativecommons.org/publicdomain/zero/1.0/>.

The new Hy logo is Copyright CC-BY-SA 4.0 Kenan Bölükbaşı, thanks, Kenan!
http://www.kenanb.com/posts/Hy-Programming-Language-Logo.html