Mahajani, like the Punjabi Landa, was used as a mercantile script (and is sometimes classified with Landa). Unlike Punjabi Landa, which dispenses with vowels altogether, Mahajani is sort of like a sloppy alphabet. It is possible to show a vowel by writing in a separate vowel glyph (not with a diacritic), but the vowel is frequently omitted. Even when a vowel is written, it can be ambiguous: “ka” + “i” can represent either “ki” or “kai”.
I described Syloti Nagari earlier as having “Semitic attitude” towards its writing system, trusting that the readers would understand ambiguous use of vowels. One might suggest that I should say that Mahajani is also somewhat Semitic, or that Syloti Nagari is somewhat like the mercantile Khudawadi, Landa, or Mahajani scripts. However, the mercantile scripts were intended for personal or family use, not for communicating with strangers.
Written Mahanaji sometimes looks like it has a horizontal “head line” like Devanagari, however the glyphs normally do not have a head line. If a head line is written in, it signifies emphasis much like underlining in the Latin script.