If memory serves me correctly we were on the FLCON6 close to DIRTY landing 9R.

The Twin Cessna was VFR South of BYRDS at 10500 (West Bound) where class B encompassed 12500. We were instructed to deviate as necessary to avoid traffic, without vectoring us off the STAR. He then requested if we could identify the tail number, without deviating from the protocol of the arrival, to let him know.

Hindsight I would have included the details to make my point. To clarify my point, I was asking if it was unreasonable for the controller to ask us to identify the tail number of the Twin Cessna. Of course we could have replied "unable" if we thought it was an unsafe request. I however, am of the opinion that his request was not unsafe, or unreasonable, given the circumstances.