I believe this window is in the logis royal (royal residence) at Loches. It's a symbol of the royalty, replete with a crown and the fleur de lys (lily flower), a favorite symbol of the French monarchy. There are also the letter C and the Roman numeral VII, standing for King Charles VII, who frequented the logis in the fifteenth century.
I read in Wikipedia that Charles VII was the first French king to reside in the Loire Valley. He also spent significant time at the Château de Chinon and in the city of Bourges. The last French king to reside in logis at Loches was François I, who is well known for building the magnificent Loire Valley château at Chambord (which is the château you see in the banner photo at the top of this blog), about 100 km northeast of Loches.