Any idea what these mean on barrel shaped shock sensors? Possibly ITEC designed.

got a pic?

Here's some photos

that type need to be vertical. Id assume that d is top keeping the sensor horizontal 

Ball bearing on a doodaa 

Have not seen those for years  the original  design goes back 40+ years   n is for normal d is damped  probably several on one cable they   will all go back to an analyser board,  as peter James says ball in a cup design the early one had gold plating and sat on 3 pins 

Used to look after loads of those, they worked fine tbf. 

Same only had issues when they had been disturbed and the trembler had been refitted back in the wrong way.

Yup, usually by window fitters thinking they were alarm men.

Then think they'll still operate if they stick them on with sticky pads...