Question I have is the last name Hreben Polish?
I Googled the term "Hreben surname" in Russian («Гребень фамилия»), and the results were pretty unanimous in stating that this is a Jewish surname, indicating an origin in the person's profession - that of a barber. In Russian, just as in other Slavic languages, the word гребень (greben', hreben, etc) means comb. It could also mean the fleshy red thing on top of a rooster's head, or the crest of a wave or mountain, but that surely is not the relevant definition here. It seems it would be unusual for a Pole, Ukrainian, Belarusian, Czech, Slovak, or Russian to have such a surname.
The town, Signevichi (Сигневичи), is located in modern Belarus, in the Brest Oblast. At the time of your ancestor's emigration, however, it still lay within Poland. In 2019, it had a population of 245 people, down from 500+ in the 19th century. Hope this helps.
Wikipedia article for Signevichi in Russian (use Google Translate):
ru.m.wikipedia.org/wiki/%D0%A1%D0%B8%D0%B3%D0%BD%D0%B5%D0%B2%D0%B8%D1%87%D0%B8