Stonehenge Aqua does not have a watermark because it is a 100% cotton machine made paper unlike 100% cotton mould made papers which have a watermark debossing within the mould.
Technically you can use either side of Stonehenge Aqua. Both sides contain the same consistent level of external sizing necessary for a watercolor paper to prevent bleed as well as allow for lifting and blending.
If you are a botanical artist or prefer very crisp lines, I suggest using the smoother side of the paper. If you work more abstract or prefer a little more texture, than you should work on the side that is slightly more rough.
Technically you can use either side of Stonehenge Aqua. Both sides contain the same consistent level of external sizing necessary for a watercolor paper to prevent bleed as well as allow for lifting and blending.
If you are a botanical artist or prefer very crisp lines, I suggest using the smoother side of the paper. If you work more abstract or prefer a little more texture, than you should work on the side that is slightly more rough.