Adjustable camisole straps.  Silk-screened by hand in the USA.
 
Sizing note:  These shirts run small.  To help you choose the right size, the actual garment measurements are listed below. 
 
If you're not sure what size to choose, compare them to your best-fitting tank top.
 
Garment chest width:
Laid flat, measured just below the arm holes.
Small:  12"    (24" circumference)
Medium:  14"   (28" circumference)
Large:  not available
X-Large:  18"  (36" circumference)