Watch List notes:

Constans II and Constantine IV. 654-668. AE follis (27.4 mm, 6.51 g, 7 h). Constantinople mint, Struck 655/6. No legend, Constans II on left, crowned, wearing military garb and holding long cross and Constantine IV on right, wearing crown and chlamys standing, facing, between their heads, cross / Large M between A / N / N / O -- X / Ч ( = yr. 15 = 655/6 ); above, K; beneath, Γ // CON. SBCV 1010; DOC 79. Rough VF, ragged-edges on flan, not unattractive for type.

Ex Leo Hamburger 1890's.

This coin comes from a large group of Roman Provincial, Byzantine and Vandalic coins which were part of Leopold Hamburger's inventory. More information on Mr. Hamburger can be found here:https://www.coinbooks.org/v20/esylum_v20n42a19.html