A list of papers which either use or mention SymPy, as well as presentations given about SymPy at conferences can be seen at SymPy Papers.
SymPy has a collection of official logos, which can be generated from sympy.svg in your local copy of SymPy by:
$ cd doc $ make logo # will be stored in the _build/logo subdirectory
The license of all the logos is the same as SymPy: BSD. See the LICENSE file in the trunk for more information.