In photos Sapele can easily get confused with Mahogany, but when you're looking at the actual boards in the flesh then it's pretty easy to tell them apart.
Sapele is heavier, harder, and darker than Brazilian Mahogany; and much heavier, harder and darker than Honduran Mahogany. Okay, Cuban Mahogany is probably similar to Sapele in weight, but when are you likely to come across Cuban in this day and age? Dig your thumbnail into Sapele and into Mahogany and you could identify which is which with your eyes closed. I bet you could tell them apart by sound as well, a bench plane runs through Mahogany with a buttery smoothness, but there's a harsher, crunchier tone when planing Sapele.
Sapele's ribbon grain can look like Mahogany in photographs, but up close they're pretty different. If you look at Sapele in a timber yard the ribbon grain often shows micro tear out from machining, but any roe or ribbon grain figure with Mahogany is more like chatoyance, and there'll be no roughness to the touch. People are often surprised at how pale freshly cut Mahogany is, it's only when the surface is oxidised that it gets darker like Sapele.
Sapele does have a smell, it's not massively distinctive, but if you sniff some fresh shavings there's a spicier note to it than with Mahogany shavings.
As Andy suggested, the problem isn't as simple as Sapele versus Mahogany, there's also Khaya which is generally called "African Mahogany", in many timber yards it just gets shortened to "Mahogany". Khaya sits somewhere between Mahogany and Sapele, but is probably closer to Sapele in it's more obvious characteristics. Again I haven't used it that much, but when I find a timber that I know isn't Mahogany, and I think isn't Sapele, then I generally call it Khaya, which just shows what a rubbish botanist I'd make!
I once sunk hours into making a pair of winding sticks out of Sapele, with elaborate inlay and marquetry work, only to see them curl up like bananas a week later. I took two lessons from that experience. One, just use MDF strips or Ali extrusions for winding sticks, and two, leave Sapele to the joinery boys.