The mnemonic RPOPQ.US has no seasonal adjustment character, or indicator in the description. Is the series (estimated quarterly population) NSA or SA?
We estimate the series RPOPQ.US from annual inputs, which by definition have no seasonality; and when converted to a quarterly frequency, still have no seasonality. The same applies to the corresponding forecast series FPOPQ.US.
It would be more accurate to describe the series as having "no seasonal pattern."
When a time series has a native frequency higher than annual (quarterly, monthly, etc.), it's possible for it to exhibit seasonal variation; if these raw figures are reported, they're called "not seasonally adjusted." Once the seasonality has been mathematically removed, the figures are "seasonally adjusted." We generally indicate this in the description metadata, in the parenthesized unit-descriptor, using the symbols "NSA" and "SA," respectively.
In many cases, we also signal the adjustment with a special character in the mnemonic (more specifically, in the concept code, to the left of the period). U.S. concept codes have an "X" near the front if they are NSA, and no character if they are SA (or do not exhibit seasonality, or are reported in only one form). International concept codes have a "U" or "A" in the second-to-last position.
Population Estimates - U.S. & State
U.S. Forecast - Baseline