You will see them 'cleaning' a flat surface or an area right on the rocks. The female gets really plump.. noticably plump and both of them get very vibrant. Even more so than normal. You will also notice the females 'ovipositor' showing. A small clear 'tube' which is what deposits the eggs. Its normally not noticable when shes not spawning.
Oh to tell the different.. females have purple ovaries which is what I find to be the biggest difference, but when they are young you cannot see this. The males have a longer 'spike' on the top fins. Females are smaller too. If you look at them you'll see that your female does not have those two long spikes like your male does when they raise them.