For orbit validation I've assumed the obvious--RF transmission. As mentioned in my SAS presentation
(
http://www.microlaunchers.com/7816/L3/sa09/sa09.html ) a small transmitter using cell phone components is suggested, with a battery to support perhaps 2 days (9 orbits = 14 hours), and allow verification via unrestricted access, reporting of reception.
A problem for US is the licensing, and that is being investigated. Use of an amateur license (I'm KD6HKU) would be illegal for a prize attempt, but could be ok for a test flight that's understood to not be an entry.
A strobe or some optical method would not require a license, but the physics suggests it would be difficult. I will do some calculations, see if it's even worth continuing with.
In any case I assume some unambiguous indepentently verifiable proof is needed.
Charles Pooley Microlaunchers