Spanish blazon: Escudo medio partido y cortado: 1.º, en campo de plata, roble de sinople, acostado de dos figuras de hombre de perfil, afrontadas, de sable y carnación, dándose la mano en actitud de saludo; 2.º, en campo de oro, torre de gules; 3.º, en campo de azur, nave de plata sobre tres ondas de plata y azur. Timbrado con la corona real de España.
I have no ideas about Q1. Q2 is similar to Castile but with the tinctures swapped. Q3 simply reflects the fact that Suances is a coastal town that once relied on its fisheries.
The monastery itself has no arms, nor indeed has the Comarca of Liébana. The nearest village is Potes, derived from the Latin "Pontes" (the bridges). The arms reflect the importance of the river crossing and also the 15th century Torre del Infantado. This explains why the tower is separate from the bridge rather than sitting on it as often seen in other Spanish municipal arms (Logroño for example).
Spanish blazon: De azur, un puente de oro sobre ondas, acompañado en jefe de una torre de lo mismo. El escudo se timbra con la corona real española.
I have to say that many of these Spanish municipal arms approved during the last 20-30 years show a singular lack of original thought. If there is an old bridge, include it; an old castle, better include that; a coastal town, better put in a boat. I have yet to discover whether there was a national policy at that time for every community that didn't already have one to have a coat of arms created for it. But if that was the case, was it the community itself who decided on the design or some authority that made recommendations?