GMC 2010 Sierra Owner's Manual page 78

WARNING:
A safety belt that is not properly worn may not
provide the protection needed in a crash. The
person wearing the belt could be seriously injured.
The shoulder belt should go over the shoulder and
across the chest. These parts of the body are best
able to take belt restraining forces.
2-36
4. Buckle, position, and release the safety belt as
described previously in this section. Make sure that
the shoulder belt crosses the shoulder.
To remove and store the comfort guide, squeeze the
belt edges together so that the safety belt can be
removed from the guide. Slide the guide onto the
storage clip.