Transiting planetary squares are likely to precipitate some sort of change, particularly Saturn or Mars squares to their own natal positions or to a crucial planet or point. With Saturn involved, it's likely to be a long lasting change. Saturn is about longterm commitment.
I had Saturn square my sun when the longest relationship I've ever been in (ten years) began. Under my next Saturn/sun square, I enrolled in my first herbalism class; I am now pursuing herbalism as a new career. The only other time in my life that Saturn squared my sun was right around my tenth birthday, and I'm not sure what, if anything, that triggered. At the age of ten, I was dealing with nasty fifth grade social dynamics, but so was every other ten-year-old, even if they didn't have a Saturn/sun square.
I have the sun square (6 degree orb, applying) to my north and south nodes, and natal Saturn trine my north node and sextile my south node, so when Saturn squares my sun, it's also applying trine or sextile to its own natal position and conjunction to either my north node or my south node.
Just typing this out, and checking past transits, I realized that when I was nine and a half, I went to nature camp as Saturn was sitting right on my NN, and that became the inspiration for work I did later. I also met a lifelong friend there, and it was my first experience with meeting someone and feeling like I already knew them even though we couldn't possibly have met before. Since my other Saturn/sun squares and Saturn/node conjunctions involved meeting a significant person or taking a new career step, I see a theme here!
If you want to figure out your Saturn/sun square themes, check your transits for your previous Saturn/sun square(s) (everyone experiences at least one by early adolescence at the latest). Think of what was going on at that time. If you've had more than one Saturn/sun square in your lifetime so far, is there a common theme that emerges between those times? Are there other planets or points that would be transited or aspected by Saturn as it squares your sun? If so, you have a mixture of influences right there.