By default, when you visualize in a diagram an element that belongs to an other model, RSx will automatically decorate the element view with a little arrow at the top left corner.
This technote explains where to find the option to disable the decoration using IBM® Rational® Systems Developer v7.0.5.x, IBM® Rational® Software Modeler v7.0.5.x or v7.5.x IBM® Rational® Software Architect Standard Editon v7.5.x and IBM® Rational® Software Architect for Websphere® Software v7.5.x
If you have two models Model1 and Model2 with two classes Model1Class and Model2Class. If you add Model2Class to a diagram of Model1, you will see the following:

To remove the decoration, go to Window>Preferences>Modeling>Diagrams>Appearance and remove the check mark from the option called Show Cross Model References as shown below:

After changing the Preference option, you will see the following in the diagram:

Note:
This option is not available in earlier version of Rational Software Architect/Modeler and Rational Systems Developer v7.0.0.x
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