When managing a property in EPiServer's admin mode there is a setting named "Display in Edit Mode". To control this setting from code in EPiServer 7 use the ScaffoldColumn attribute.

When set to false it will hide the property from editors, meaning that while they may seem the rendered value in preview mode they won't see a blue box around it and they won't be able to click on the property to edit it. The property won't be visible in forms editing mode either.

There is also the Editable attribute. When this is set to false the property will still be visible to editors in both preview mode, with a blue box around it, and in forms editing mode. The editor for it will however be disabled, meaning that while editors can inspect the property's value they can't modify it.