Yes, desktop AT cases in the i80286/i80386 era came with
the Turbo button and a Turbo LED - replaced by a two-digit segmented display in i80486 era mini-tower cases; you would
"program" the segments with jumpers to display CPU clocks or the letters "HI"/"LO".
The 8 segments were lettered A-G clockwise, and each segment could be set to one of the 3 modes - turbo only, slow only, and both - or left unconnected for always off. This would allow values like 20/40, 25/50, and 33/66 MHz typical for the Intel 486DX/DX2 series and
clones. There were also variants with additional leading "1" which could display 50/100, 60/120 and 66/133 MHz used by Intel 486DX4, AMD Am5x86, and Cyrix Cx5x86 processors.
The default mode (jumper open) was indeed turbo speed (at least on "no-name" i80486 motherboards with an UMC chipset).
Anyway this feature didn't make much sense by 1990s - most i286-era games were using
programmable interrupt timers, so they ran just fine on significantly faster i386/ i486 processors.
I don't think turbo switch was ever implemented on Pentium/MMX (P5/P54) motherboards based on
i430 chipset series, and in 1995 the ATX form factor appeared which did not specify a turbo switch either.