There's a group of hatpins out there that are excellent fakes.  Most collectors end up having a couple of these in their collections because until you know better, these hatpins appear to be great additions to your collection.  These are known as the stamped metal hatpins or "Braverman" hatpins to experienced collectors.  They are made of brass and are simply machine stamped over a mold.  They typically have a bronze-color finish to them in order to make them appear old.  The pinstems are nearly always 9-inches in length and many are ever-so-slightly thicker than original pinstems.  Some pinstems, but not all, come to a more abrupt point than they should too.  The findings (small finishing pieces used to cover the connection of the pinstem to the ornament) are close in design to an original finding but are in fact modern.  Remember this shape because those findings are ONLY found on these fake/reproduction hatpins.  Also, the finding and pinstem are typically the same bronze color of the ornament.  This isn't typical for pinstems though findings should usually match closely in color to the ornament.  Oftentimes these hatpins will have the finding off-set from the center of the back of the ornament too which is an excellent clue to the hatpin being a fake or reproduction.  On an original hatpin, if the finding couldn't be set directly at the center back of the ornament, then a bridge set-up would have been used in order to do so.  Any hatpin that has it's finding set to one side is a fake. 

These machine stamped hatpins come in dozens of designs (a couple of styles are actually molded rather than stamped but they share the same finding and finish).  The most common designs are:

Art Nouveau lady face with wind-blown hair, Art Nouveau nude lady, cupid with bow and arrow, scotty dog, 4-kitten, hunting scene (man and dog), 2 horse and riders, scarab, Indian brave (or maiden), Indian Chief, owl,  and many, many more.

Some that are found with glued-on rhinestone accents include: horsehead with red rhinestones, court jester/clown with multicolored rhinestones, flower with leaf with blue rhinestones, artist palette with multicolored rhinestones, floral design with multicolored rhinestones, etc.

Included are a couple that are molded rather than stamped but with the same modern finding:  art deco lady with pearl headdress, and a butterfly.

These fake/reproduction hatpins are great for costume purposes but have zero collectible value.