In reply to cb294:
That is convention but that does not apply to Adršpach. Adršpach is nature reservation with the highest level of protection. Except for marked routes even entry is prohibited. Climbers have an exception under certain conditions and of those conditions is no chalk. If climbers don´t respect these conditions there could be complete climbing ban imposed in the area (parts of Adršpach are closed already)
There is Křížový vrch just across the road (and quite a few other areas in Czechia) where chalk is not banned by authorities and climbers can really break convention only