Hi Catcuddler,
There is a very easy way to find out if your cat is in season.
Just stroke her along her back from the base of her neck to where her tail joins her body. Use slightly more pressure than for ordinary stroking. If she is in season, as the pressure reaches just in front of the root of the tail, she will arch her back end up returning pressure against your hand. This is a sure sign that she is ready to mate, that is of course if she hasn't been spayed. The miaow is generally quite different than an ordinary miaow, it's more like a wail, louder, and very persistent. Trying to wee everywhere may be because she can't get outside. If she is in season, don't let her out if you don't want her to have kittens, and have her spayed as soon as the season is over. By the way you didn't say how old she is. The first season can arrive as early as 5 to 6 months. Another thought, even if a cat has a litter tray, and it is in season, it often won't use the tray, and will kick up all sorts of performance in order to be let out. Hope all goes well. Please let me know.