On the very early Classic Mini and Morris Minor the indicator stalk had a little green plastic lamp cover with this bulb fitted underneath.

Whilst the indicator stalk was being used it would flash in synch with the external indicators.

Although the design was a little quirky it was a simple design that worked far better than the flashing lamp you get in modern cars, you simply cannot miss the flashing lamp when you are driving along so avoiding indicating as you drive along....  wish we still had them, it might help to avoid a lot of RTA's at junctions and roundabouts.

This bulb is also  used in the later rocker switches