The Parker Pen company has been making fountain pens since 1889. As you can imagine, Parker has made many fountain pen models since that time. Yet there are a couple of sure-fire ways to identify a Parker fountain pen. Knowing how to identify a Parker fountain pen is beneficial because a great many of them date far back in time and have relatively high monetary values. Plus, knowing a fountain pen is a Parker helps you to replace parts for the pen.
Check the design of the pen clip for the most prominent part of the Parker logo: an arrow, complete with arrowhead and vanes. If the fountain pen has a pen clip, and it is in any way designed as if it is an arrow, almost certainly it is a Parker fountain pen.
Check the barrel, cap or metal band of the pen for the Parker name. Some Parker fountain pen models use the Parker name on the aforementioned pen parts.
Open the fountain pen. Check the ink cartridge itself inside the barrel for the Parker name and logo.
Check for an "H" in a rectangle that's stamped on the pen, in much older pens that are overlayed in gold. The "H" stands for the George W. Heath company of New York, which did the gold work overlay on turn of the century Parker pens.
Memorise the names of the complete line of Parker fountain pens and how each one looks, starting back in 1889 through today. Earlier pens, such as the Parkette, aren't easily distinguishable as a Parker pen by the arrow clip. The Parkette simply says it's a Parkette pen on the barrel, so knowing the Parkette is a Parker pen is how to identify that particular fountain pen model from Parker. Go to ParkerPen.net and click "Penography" for an exhaustive list and pictures of Parker fountain pens.