Two historic Mongolian scripts, Soyombo and Zanabazar Square, have been proposed for inclusion in the international character encoding specification ISO/IEC 10646. There are two contrasting designs of the coded character sets for Indic scripts—the virama model and subjoined model—but the designs of the proposed character sets are a combination of the two. Furthermore, the designs for the two scripts are different in several respects. In this article, the proposed designs are analyzed and the backgrounds of the differences are described. Some of the differences can be justified by the different natures of two scripts, but others cannot. Further research into the two scripts is required for the stable design of the coded character sets.