I'd echo Mandy's post - raise a few to slaughter a couple of times til you get to know the in's and out's, it will save so much hassle, head scratching and heartbreak.
For example, what age are your breeding gilts, have they had erysipelas vaccines, wormed ? (orally or by injection ?) Lots to think about and LOTS to learn - you can't just stick em in a field and leave them to it. Again, AI'ing at this time of year - unless it's pedigree breeding stock that you're going to grow on til next spring before selling your market will be quite limited, AI now, piglets born September, ready to sell November (it's not really weaner buying time then
)
But to answer your question - there will be clear signs of season. Her vulva will be swollen and red and she'll stand rock steady when you put pressure on her back. There's no point "getting stuck right in" when she's not in season - you'll only hurt her, freak her out and end up stinking of pig semen
Hope that helps ?
Karen