OK, just to get things straight on sights, this is looking at the slide from the rear:
S&W: install right to left. Remove, left to right. BTW on S&W 1-3rd generations, beware of the spring for the magazine safety and firing pin block spring and plunger as the rear sight moves to the right. On the M&Ps, beware of the striker block end cap, spring and plunger. Make sure the set screw is removed before trying to get the sight off. It can catch in the recess for the cap for the striker block. Be very careful in installing the sight so you don't bugger the various springs up.
Colt: install left to right, Remove right to left. On 80 series be aware of the spring and plunger for the firing pin block. Again, be very careful of the spring when installing the sight.