The Mahal style gets its name from a village in Western Iran. It's in the Arak district, famous for weaving rugs for centuries.
Although Mahal designs come in many different configurations, the most characteristic Mahal is probably going to have an all-over pattern in the rug's field. Medallions are rare. This concept is easy to see in the examples below.
Moreover, unless it's an antique, a Mahal styled rug was probably made in India. Most rug-buying countries have embargoed goods from Iran.
Mahal Ivory/Light Green
Vines and flowers arranged in a regular pattern in the ivory field of this rug proclaim it a Mahal.
One has the sense that the field of this rug expands outward forever and ever, repeating the vertical and horizontal flower/vine design. The border frames a particular set of elements, chosen perhaps for perfect symmetry.
The strong neutral zone prominent in the all-over typifies Mahal design. The flower/vine elements are also tell-tale.
Mahal Rust/Navy Blue
The designer of this Mahal makes a color statement with bold red and black backgrounds. This is a sharp contrast to the neutral-based schemes above.
The colors for this rug produce a totally different feeling, but as you can see, Mahal motifs are everywhere.