Write an OnGetGutterImage event handler to control gutter objects (TCustomGutterObject) for the specified line. List contains all gutter objects (from the Gutter.Objects) and bookmarks (from the BookmarkObj) associated with the Line. If you remove some of them from the List this objects will not be displayed (and processed) on the gutter. 

You may add any custom gutter object (object of the class that is derived from the TCustomGutterObject). After processing this object will be destroyed by the syntax memo, so you don't have to destroy objects that you add to the List.

TCustomSyntaxMemo Events