With the aluminum 52T Biopace that came with road bikes, behind that yellow logo is just the same three sided cutout you can see on the rest of the ring.
Dunno about the steel Biopace triples that came with some mountain bikes. The few bikes I've seen with the steel Biopace were rusted so I didn't bother with 'em.
I left the yellow sticker on for reference while I was experimenting with re-orienting the Biopace rings. After some trial rides I like the big ring oriented one tick away from the original position -- feels more natural with my cadence. But the same trick with the little ring felt weird, with dead spots and herky-jerky cadence. So the big ring is oriented a little differently from the factory spec, but the little ring is back to original position.
For several months I've ridden the 52/42 Biopace on my 1993 Trek 5900, with various 7-speed freewheels (old set of wheels from an Ironman, not the original wheels for the Trek). They're a little different, including being picky about cross chaining. That might be due to the different wheelset. I can use all 7 speeds with the little ring, but with the big ring I can hear a little chain noise any time I'm out of the 3 smallest cogs. Occasionally I'll shift to the larger cogs while still in the big ring, mostly while standing to climb, but the chain noise tells me it's inefficient.
I'm about to swipe a conventional 53/39 chainring set from an old aero TT bike with cracked frame that I'm cannibalizing for parts. So it'll be interesting to compare a conventional double with the Biopace.
I might also try some 175 crank arms. I've been using 170 on the Trek and I'm betting the Biopace will work better at lower cadence with a bit more leverage from longer cranks.