I catch the drift, @SergeantQueen and agree with your conclusion (round) – but for different reasons:
The letter S is curvy and slinky, not a single line – which makes a point for a circle.
Same with O – it is a circle right there
Similar with U—the based of the U is rounded. Again, suggestive of a circle.
And the P – well, there is a straight line, but the curvature of the upper portion also suggests a round, not a linear shape.
For all these reasons – Circular tupperware.