So far as I have ever been able to determine, there does not exist a
non-pyrotechnic device that is conveniently attachable to a PFD and
meets USCG regulations regarding visual distress signals.
(http://seayaks.home.att.net/CoastGuardPage2.htm)

Is anyone aware of such a product?

I am aware of the product by ACR Electronics, but that thing seems way
to bulky.

The VIP Signal Light, which you may also be aware of, does not meet USCG
regulations.

I just became aware of http://www.greatlandlaser.com/ and their rescue
Laser Flare. Apparently they do plan to release an SOS version that
would meet USCG regulations. I doubt they would mind some further
encouragement from those who would be interested in what may be the only
product, which is not bulky, to do so.