Add an indicator somewhere that's always visible that displays the current status of the Snap-to-Guides and Snap-to-Document-Grid controls. It could also act as the on/off switch for them.

Now there's no way to tell if the snap-to mode is engaged or not without either dragging something around to see if it snaps-to a guide or grid, or going into the View > Grids & Guides pull-down menu.