I wish I had more information about Markos Sifnios, but as there is only been a recent resurgence of interest in his collaborator Marika Papagika and I’m not in a position to be doing extensive research into her career in the US during the earlier part of the 20th century (yet).
I had first come across Sifnios’ work when I found this wonderful youtube video (see below) of a tune called Smyrneiko Minore (Smyrnaean Air) which, given the date (1919) here (if it is correct) would coincide with Papagika’s first recording in the states with Victor Records.
There is a brief snippet about Sifnios’ collaboration with Papagika at the Wikipedia entry which I can’t really verify or attest to the truth of though interesting in its own right:
Cellist Markos Sifneos [sic] collaborated with Marika Papagika on at least 24 separate occasions. Aside from Kostas, he is her most frequent collaborator, and was one of the few people to play cello on Greek recordings before World War II. There are no records of him recording with anyone except the Papagikas as Cello was not an acceptable instrument for Greek music at the time.
So I came across this video and though I had already known about Marika Papagika I knew nothing about the fact she had a cellist in her Greek band. So that was something of a revelation. I doubt cellos were typically a part of traditional or folk Greek ensembles as the above quote seems to indicate, and more than likely, as is the case with Klezmer and other folk music ensembles (and “pick-up” bands in general) Sifnios and his cello just happened to be at her disposal. But what this also says is that Sifnios could be considered one of the first “Alternative Cellists” in the US (if not the world).