No, it's not strictly for macro. It's a zoom lens that's really bad for macro, but much more capable than other lenses with similar specs.
With Sigma, if the lens is capable of a reproduction ratio of 1:4, which means that a subject that's the same size as the sensor will fill 25% of the frame, then it's a "macro" lens. They should label it quasi-macro or somewhat macro, but they don't. If you want a real macro lens, you need a lens capable of 1:1 "true lifesize" reproduction.
This also means that you can't just walk up to a subject, zoom in to 300 mm focal length and expect to get the closest photo ever. It just won't focus. Every lens has a range where it won't focus on the subject. If you use this lens 70-300 mm lens at 70 mm, the minimum focusing distance might be 40 cm away or so, which means that the lens can't focus if you stand at 27 cm (just an example). And if you stand at exactly 40 cm distance and then zoom from 70 --> 300 mm, you won't get better macro, because the minimum focus distance becomes much further away.
I have a Sigma 24-70 mm f/2.8 "macro" lens. It's fantastic and does everything I need it to do. I use this lens for around 90% of my photos because it's very sharp, even at f/2.8. It's capable of 1:3.8 reproducibility, and while it can't give me 1:1 reproduction, I find that I rarely do that with a lens capable of 1:1 anyway.
Tamron lenses are usually as good or better than Sigma lenses (in terms of optics), but their build quality is always poor in comparison. I buy Sigma. I'm strictly talking about Sigma EX lenses (top grade lenses) and comparing them to Tamrons of similar price, because I've never looked at the cheapest end. Many Sigma EX lenses are as good optically as the equivalent Nikon or Canon lens, even "L" lenses, but they're usually noisy because they almost never have SWM/USM for quiet, fast focusing, and the AF has to hunt in low light, although my Sigma 24-70 doesn't do this and also focuses fast (but noisy). That's too bad, although you ARE paying 1/2 price for it, so cheer up.