What does "(S)" mean in the US Census data of surnames?

I am working on a project using some Netflix catalogue and some 15000 names of actors/directors, trying to estimate their ethnicities using datasets of names and what ethnicity they are most common in. I found the US Census Data of surnames and % of people who identifiy as certain ethnicities, but it’s riddled with “(S)” values amongst the legit floats. Unfortunately the data dictionary does not clarify things.

Does anyone know the significance of that value?

Update: Apparently it’s indicating that there weren’t enough responses so to protect their identity the exact percentage is not given.

For my purposes I just treated as 0, since other columns were sufficient to gather the most likely ethnicity for the given surname.