They have the shape of the Maltese cross and remember quite well the consecration crosses and crosses of cemeteries in 12th century.
There is reason to believe they were the formula of absolution pronounced by the priest to the patient receiving the sacrament of Extreme Unction.
From Bouteilles, 1857
Musée départemental des antiquités, Rouen - Inv. 2006.0.628
From Rouen, 1869
13th – 14th c.
Musée départemental des antiquités, Rouen. - Inv. 1691.6 (D)
For further details :
Favreau/Michaud. Corpus des inscriptions de la France Médiévale. 2003. N° 246 p 323