Diogenes' masturbatory episode is referred to darkly by Bertrand Russell in his tome A History Of Western Philosophy, in the following passage:
The cynics thought that one should be without shame, and Diogenes would have none of it, wishing to be in all things like a dog; yet even he, after one attempt, abandoned, in practice, this extreme of shamelessness.
(The word 'cynic' is derived from the greek for 'dog'.)

Diogenes is also known for wandering around Athens carrying a lit lantern, in bright daylight. When challenged as to his purpose in this, he's said to have replied: "I'm looking for an honest man."

Thus, he's often depicted alongside a dog, and holding a lantern.