The only other Tiger I've seen had chimes. There is one on you tube that has chimes and IPDB shows a picture of the chime unit. So this may be a hack. Maybe by an individual or an importer. Notice the three holes in the cabinet where the chime unit would have attached.

Altered to stimulate interest adding more plays so more income.

Or the games were imported less the chime units and the circuit board & speaker is cheaper than a chime unit.

The famous parts supplier WICO sold a sound board in the 1970s whose purpose was to make EM games have the modern, up-to-date sound of first-generation solid-state games. Call it a "mod" if you wish.
.................David Marston

Did it come with a banner to put under the playfield glass? I've often wondered about this game:
Space Mission Electronic Sound (resized).jpg
/Mark

It may be awhile before I can retrieve the pertinent WICO catalog to answer about the banner.
.................David Marston

David, that sure looks like a Wico decal.

I owned a gottlieb tiger a few years back. had the standard gottlieb chime unit in it.

one of the largest distrubtors here in australia towards the end of the e.m. era, they had a small circuit board and speaker installed to all of their pins.