This is the 2400th most frequent Polish word.
znaku
"Znak" in Polish means "sign" or "mark," and "znaku" is its genitive or locative form.
This usage refers to a road or traffic sign, as 'znaku' is the genitive case of 'znak', meaning 'sign'.
Na znaku drogowym widniał nietypowy symbol.
On the road sign, an unusual symbol was displayed.
'Znaku' here indicates a 'sign' as evidence or indication, in the genitive case to express 'of what or whom'.
Nie widziałem żadnego znaku jego obecności.
I haven't seen any sign of his presence.
In this sentence, 'znaku' conveys a figurative 'sign' or signal from fate, also in the genitive case to express possession or relation.