Before the war the border had been far more eastern.
I have only visited one border town recently: Guben/Gubin, a bit south of Frankfurt/Oder.
I found border markers on both sides of the river here.
They seem to be hollow and seem to be made of wood/plastic.
407 (D)
407 (D)
407 (PL)
407 (PL)
The only other visit to the German-Polish border was all in the south at the tripoint with Czechia, back in 2013.
CZ-DE-PL