A Shield is easily carried in a pocket holster. It is considerably smaller than a Glock G36 (or other sub-compact single-stack), which IMO is about the maximum size. I have a Springfield XDs .45 ACP which is nearly identical in size to a Shield. The Springfield Mod 2 is double-stack, and only 1/8" larger than the XDs, with 9+1 capacity in .45 ACP.
Pocket carry may not be the best for a quick draw, but you can put your hand on the grip in a questionable situation without betraying its presence and escalating the encounter. It's just as fast as a belt holster from that condition.
The DeSantis Nemesis comes in a size suitable for a Shield. The Nemesis is sticky on the outside and slick on the inside - almost too slick for good retention. Galco makes a leather holster in several sizes, rough side out. They're a little large, but fit all but the most European cut pockets. Ryan Grizzle (and others) custom-make leather pocket holsters which are no larger than necessary.
My current favorite is a Kydex holster by Detroit Holsters, which completely covers the rear sight and trigger guard (and has room for a LaserMax Micro).