Were the rear sights nickel also?

While I have never actually seen one in person, these pictures would suggest "no".

Post #5 here

The ultimate Highway Patrolman thread.including N frame ser# ranges

and this

Florida Highway Patrolman 28

I can say that since I have never known S&W to nickle the rear sight on any other model, it is very doubtful they would here, but factory nickle HPs are rare enough anyway.

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I need ammo, not a ride.

I think we can safely say S&W never nickel plated a revolver's adjustable rear sight.

Model 28s with original factory nickel are rare and valuable. Model 28s with after market chrome and nickel plating are common, and to collectors are just "shooters." The only thing more common are used guns falsely advertised as rare and valuable.