I've never heard of such a feature on manual cars, only the park/neutral starter interlock on automatics. I know we all have different habits regarding manuals. Mine is to ensure the car is in neutral and to start it without depressing the clutch pedal. Unlike some, I also prefer to park manual cars in nuetral rather than in gear. This avoids transmission damage if the car gets hit by another vehicle (eg. when parked on street). If I have concerns as to the reliability of the parking brake (eg. on a hill) I will turn the front wheels into the curb. Only in a situation without a curb or similar on a steep hill will I leave the car parked in gear.

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107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.