The surname Piaszczyński is among the co-coat of arms of the Ostoja coat of arms.
Coat of arms legend:
In 1069, Bolesław the Bold gave the Ostoja coat of arms to a certain knight.
This knight captured the advance guard of the pagans, and one of the captives promised him
swearing by the sun that in exchange for freedom and the coat of arms he will help destroy the rest of the enemies.
He returned to his people, reassured them that there were no Poles in the area,
and one by one introduced the pagan troops an ambush set by Ostoja.
When the reinforcements arrived, Ostoja attacked the foreshores on uninsured enemies
and for a week Poles cut down pagans from quarter to quarter.
As a reward, Ostoja received a coat of arms with two months (crescents) and a bruised sword.
Marek Derwich, Marek Cetwiński, Coats of arms, legends, ancient myths, p. 73

Ostoja. Que duas lunas defectuosas ceruleas dorsis contra se rendentes,
cruce etiam cerulea illas intersecante, in campo rubeo defert.
Jan Długosz, Insignia ..., nr87, s. 61-62

Which two partial wax [golden] moons are placed opposite each other with their backs,
and with a wax [gold] cross, these [moons] cut through, represent in a red field.
Translation by Danuta Szopa