Date of Birth? 
For a rook of vis I'll give you his address and true name!
Payback for making it so hard to become a mage in that underdark campaign!
I don't see Diedne Magic as being innately different from Hermetic spontaneous magic. For one, there is nothing in the entry for the Virtue that mentions it uses strange rites. The Diedne might have been a house that used strange, disturbing practices, but they were the contributors of spontaneous magic to Bonisagus in the first place.
What they are is effective. The spontaneous magic a character possessing that Virtue would cast would always be highly effective, beyond and above the norm. It is also likely that their gestures and the like would be more complex, perhaps with secret signs put in. It is clearly the kind of Virtue one gains during the Apprenticeship (rather than a mystery), and I would speculate that it is more a formatting of the magi's base Hermetic technique than a "special method" they use. To recognize it would take;
a Vim specialist analyzing the yield of the suspected magi's spontaneous magic
a Peception + Magic Theory + stress die roll against an Ease Factor of 18 (higher if the magi is going to effort to mask their magic somehow). This ensures that only a true student of Bonisagus' Theory could notice, and only if they were looking for it (add 10 to the Ease Factor for just "gee, that looked odd")
This is no personal prejudice or love of the Diedne. The flaw is a Dark Secret, not "easily noticed". Being discovered to be a student of Diedne is an offense punishable by death, censure and other horrible things, therefore it shouldn't be trivial to spot.