You can display the «constraint» keyword directly on BDD or as a "secondary stereotype" on a Parametric Diagram.
Typically, a ConstraintBlock either has an equation for its constraint parameters, or it binds them to child constraint properties (that are each typed by a ConstraintBlock). It is any case clear what it is for, mathematics.
If you must use an indicator, a prefix 'Eq' is sufficient and reads well. Example: EqIdealGas
.