For general annotation on the METSIM Model Diagrams the Text Box is ideal (refer to technical note on using text boxes for annotation).
But sometimes you may want to associate the annotation with specific unit operations, and you may want to display some APL characters (such as to accurately describe a mathematical expression).
In such cases you can use the fact that the Unit Operation Name field can contain multi-line text and APL characters, using the semi-colon as the new line code.
For example, you could use the Unit Operation Name field to store and display a complete specification:
Name: MyPump1;; Capacity: 300 m3/h;; Head: 20 m
which would display under the Unit Op as:
Capacity: 300 m3/h
Head: 20 m
Note I used two line feeds (two " ; " characters ) to make it look better when only one is necessary.
And you may be aware that there are other better ways to create and store equipment lists, and that having additional information stored in the Unit Operation Name may mess up the intended use of other reports etc. - but this may be a trick that is useful in some specific cases. I sometimes use a MIX, with no streams connected (and turned off to prevent errors) as an object to hold and store annotation in this manner.