Dash button
 

I was looking at a W126 560SEC and on the lower console by the gear shifter was a button with an exclamation looking symbol pointing sideways. What does it do?

is the button red?

city/country horn switch. Push it and blow the horn, it should be louder.

For those scary mountain passes where whoever honks first has right of way.

Interesting feature. Was it always an option on the W126s?

The two tone horn was optional equipment for W123s, W126s, W201s, early W124s and I believe early W140s.

And by two tone I mean selectable town or higway tones (as mentioned before by 79Mercy), as most Benzes do come fitted with a two tone horn standard (high and low tones that sound together).

Basically, the town/city horn was a single or double electric unit and the highway/country horn was air operated (which sounded much more louder).

Even earlier...my dad's 71 280SE has that feature...