Unable to answer "What kind of memorial is this?" for https://osm.org/node/2424692546 via StreetComplete 53.3:

It's a cross on top of a plaque.

On the front:
"Cruzeiro da Independência"
"MCMXL"
"VIII Centenário da Fundação"
"III da Restauração de Portugal"

On the back:
Come see to find out! There's a text by Pe. Moreira das Neves