ations ▁ ▁The ▁study ▁of ▁post marks ▁is ▁a ▁special ized ▁branch ▁of ▁phil ately ▁called ▁marc oph ily . ▁It ▁may ▁bring ▁added ▁value ▁to ▁the ▁st amps ▁by ▁their ▁historical ▁significance . ▁Other ▁parameters ▁are ▁the ▁r ar ity ▁and ▁the ▁attract iveness . ▁In ▁particular , ▁the ▁st amps ▁issued ▁by ▁the ▁Empire ▁of ▁Austria ▁during ▁the ▁ 1 8 5 0 - 1 8 6 7 ▁period ▁( the ▁ 5 ▁issues ▁before ▁the ▁Aust ro - H ung arian ▁comprom ise ▁of ▁ 1 8 6 7 ), ▁are ▁collected ▁for ▁their ▁variety ▁and ▁beauty . ▁More ▁details ▁can ▁be ▁found ▁in ▁Val u ation ▁of ▁can cell ations ▁of ▁the ▁Aust rian ▁Empire . ▁ ▁A ▁special ▁or ▁rare ▁post mark ▁can ▁substantial ly ▁add ▁to ▁the ▁value ▁of ▁a ▁stamp . ▁ ▁Also , ▁in ▁addition ▁to ▁every day ▁post marks ▁there ▁are ▁post marks ▁indicating ▁the ▁first ▁day ▁of ▁issue ▁of ▁a ▁particular ▁stamp ▁and ▁p ict orial ▁can cell ations ▁comm emor ating ▁local ▁events , ▁anni vers aries , ▁and ▁the ▁like ▁and ▁s log an ▁post marks ▁which ▁advert ise ▁an ▁event ▁or ▁pass ▁information ▁to ▁the ▁public . ▁ ▁( There ▁has ▁been ▁a ▁recent ▁change ▁to ▁the ▁term ▁" p ict orial ▁post marks " ▁rather ▁than ▁" p ict orial ▁can cell ations " ▁by ▁the ▁US PS .) ▁ ▁There ▁are ▁some ▁examples ▁of ▁" f aked ▁covers " ▁produced ▁by ▁phil atel ic ▁for gers , ▁most