This shirt is vintage with a bright floral pattern.  It does have a mark on the back.  The fabric is 65% polyester and 35% cotton.  The tag says one size but I believe it is M/L due to the measurements.  
It has overall wear from use.  This wear can include pilling and snags.
Measurements are approximate and in inches.
Pit To Pit: 21
Shoulder to Shoulder: 21
Back Length (from top of collar to bottom of shirt): 28.75

Please look at pictures for more details about the item.