Kotwica – Wikipedia

However, it was soon abbreviated to the letters PW, which over time came to symbolise the phrase Polska Walcząca (“Fighting Poland”). Early in 1942, the AK organised a contest to design an emblem to represent the resistance movement, and the winning design (pictured) by Anna Smoleńska, a member of the Gray Ranks who herself participated in minor sabotage operations, combined the letters P and W into the Kotwica.

: https://en.wikipedia.org/wiki/Kotwica