Here is Antigua 1903 2p Seal of the Colony (Scott 23) with Crown and CC watermark and a partial margin watermark. You can see a vertical line on the right, and a partial circle along the lower right edge.
Based upon the image shown in this thread, http://goscf.com/t/68695
, I suspect I'm seeing the bottom part of the "C" in CROWN of the margin watermark. (Edit: It could be the top part of the "C" too, depending on the direction of CROWN.)
If I'm off the mark, please let me know.