My general observations are...
Hinds tend to be hefted and so will hold around the same area. The science says that they actually hold in very small areas of only a few acres generally speaking. Smaller spiker stags will tend to be found on or around the same ground as the hinds throughout the year though they seem to live separate from the hinds but a lucky spiker will cover a hind and try to hold hinds into February. I'd be very surprised if you are seeing hinds and there aren't a few spikers in the same area, though maybe not in the exact spot that the hinds are choosing to appear but certainly within a few hundred yards.
Young, but fully grown, stags tend to be the first animals to move onto "new" ground where there have never been sika before and it may be years before hinds appear.
The larger stags, as Nick has said, often live totally solitary lives and are extremely wary so even where they do associate with the hinds throughout the year you will do well to see one. My observation is that a very small number of, often, very large stags will stay in or around the same area as the hinds all year and if you want to see one you will lie for many days with a big spotting scope, don't ask me how I know this
The rest of the stags tend to move off the "hind ground" once the rut is over, and some of these will also be big stags.They will disappear literally overnight. In my case, on several bits of ground a considerable distance apart, the stags move back in on the first week of September. You could set the clock by them and no external factors seem to impact upon the timing. Their move back in is interesting as with the help of trail cameras I've observed that they tend to return to certain specific areas in the first instance and for 1 - 2 weeks they will stay there apart from the hinds. I can't say that they are in groups, but there are certainly numbers of stags in close proximity. It is almost like this ground is a "staging post" before they move on to their rutting ground. About the middle of September they will then move to their rutting grounds and the "staging post" grounds will be totally empty. So, ground full of stags in the first week of September does not always make a good spot to look for one later in the rut.
If you are seeing hinds by the road side then there is either a huge density or they are not being disturbed. Sika are extremely wary and in most places are almost nocturnal. Stags, except for the spikers, are even more wary and before breaking the tree line they will usually stand and watch other deer for a long time. Except when they are moving between areas, during the rut for example, I've never seen a stag by the road and even then they were only crossing.
In general stags look different to hinds in the same way as red stags do plus for most of the year sika stags will be black in colour. The bigger stags are cast by the end of April with me and the younger ones are starting to go into summer coats around that time as well - I shot a young stag 2 weeks ago that was looking very ragged as he was in the process of changing coats.
One other factor worth considering is that sika migrate. I know this sounds like the start of a Monty Python sketch but research in Japan has shown that during winter if they get deep snow or limited feeding then sika hinds can move out of an area completely. In one area I shoot over it is my view that this happens to a greater or lesser extent during some winters and there was one particular year when the area just emptied. The date of departure is extremely variable but they tend to return on the second week in March no matter what. So, although the hinds are hefted under some circumstances I am convinced that they will move out for periods ranging from a month or two to, in one instance, over 4 months. In my area I believe this is driven completely by food supply.