Grip safeties occasionally turn up on early pin-fire game guns, and on conversions from percussion. There appear to be several patents involved.

Here is a Harris Holland 12-bore, no. 824:

[Linked Image from i.imgur.com]

A Hugh Snowie 14-bore, no. 3277:

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A 16-bore conversion to pin-fire from percussion, unsigned:

[Linked Image from i.imgur.com]
[Linked Image from i.imgur.com]

And here is an unusual variation on the grip-safety idea, on a 16-bore pin-fire signed Robert Marrison of Norwich, no. 2281, with an action by Jean Louis Mathieu Godin of Herstal, Belgium, itself a copy of Beatus Beringer's peculiar underlever action. The safety is a small stud protruding behind the hammers, and the triggers cannot be pulled if the underlever is not correctly in place and the stud is correspondingly depressed:

[Linked Image from i.imgur.com]
[Linked Image from i.imgur.com]