how do you attach indicator discs?

[mickster04]

Hey team. I have a steam engine I want to put indicator discs on but I don't know if they're supposed to stick in or just be glued in position. Brake pipes have holes to stick into see.

I am modelling70/80/90s ish  so figure for a preserved train it should be express (domino) settings like (hopefully) below.
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0 - 0


TIA!
Mike

[Railwaygun]

Use white glue / PVA /  clear glaze or tacky wax - will allow easy removal / replacement