This month the declination of Mars gets so high that it is beyond the limit set by the Sun, so we say that Mars is "out of bounds." During this time, Mars will have more freedom than usual to accomplish Marsy types of endeavors. On the high end, this could be a great time for groundbreaking work, pushing forward an innovative agenda at work or in your creative endeavors.
At the low end, when a planet is out of bounds in a natal chart, it can relate to the person being seemingly unable or unwilling to question their own desires. Mars is the planet of "I want." So when transiting Mars is out of bounds, it might be that we are less likely to question what we want, and to take actions we might regret later, when Mars comes back into "normal" range.
So my advice is that once Mars is out of bounds, run any off-the-wall ideas by those close to you. If you're getting a lot of negative feedback, take it into account, and consider scaling back your plan.
However, if fear is your only obstacle, and you're working on something that has the potential to push boundaries in a good way, for instance, in a direction that will give people more freedom of personal expression, this might be great timing.
The Technical Details
Mars will be out of bounds from May 15 through June 30.
When Mars goes out of bounds on May 15, it will be in the sign of Gemini. On June 5, Mars enters the sign of Cancer. So while Mars is out of bounds it will move through the "regular" degrees (longitude) of 16° Gemini through 16° Cancer. Take note if you have natal planets between 16° and 29° Gemini, Sagittarius, Virgo or Pisces, and between 0° and 16° degrees of Cancer, Capricorn, Aries and Libra. Mars will aspect those degrees during its out of bounds tour.
When we start using declination, it's easy to confuse the numbers. The degrees in your natal chart measure longitude. They are different from the declination degrees, which you'll find listed on a declination grid. So if you're looking at your own chart and transits, make sure you're taking into account both numbers.
During this out of bounds cycle, Mars will make a few aspects with other planets (by regular longitude). In terms of world affairs, this could lead to some colorful public displays of conflict, especially near May 29, when Mars opposes Saturn in the "idea axis" signs of Gemini and Sagittarius.
Just before it goes out of bounds, Mars will square Neptune on May 11, and trine Jupiter on May 12. Then it goes out of bounds on May 15, after which it makes a quincunx with Pluto May 19, opposes Saturn on May 29 (at 25 degrees). Then Mars forms a sextile with Uranus May 30, squares Jupiter on June 25, trines Neptune on June 26, and conjuncts Mercury on June 28. By the time Mars opposes Pluto on July 2, it will be back inside the "normal" limits of declination determined by the Sun's upper limit. That's probably good news.
In my out of bounds research I've focused on natal chart significations, and haven't spent quality time looking at world events. So I can't say anything definitive about what to expect. But in thinking about what transiting Mars out of bounds could signify, I'd start by thinking about Saturn. Here's why. You might know that Saturn never goes out of bounds. So it's interesting to consider that when a planet is out of bounds Saturn can't make the strongest aspect to it (which is a conjunction in combination with a parallel). Metaphorically I think this carries some weight. Because if Saturn isn't able to set limits in the strongest way (by making the strongest aspect), the out of bounds planet has that much more freedom to carry out its agenda.
For an example of the strongest type of conjunction in action, take Cameron Diaz, who has natal Mars conjunct the Sun and also parallel. We can see the strength of this aspect play out dramatically in nearly all of her film roles, from the action-heroine in Charlie's Angels, to the predatory vixen in The Counselor. I've been collecting great Sun-Mars one-liners from her films. Here's a good one from the comedy The Other Woman: "Cry on the inside like a winner."
Thinking about this month, on May 29, when Mars is at 24°N13' declination, it will also be 25° 39' Gemini (longitude). It so happens that on that same day, Mars will oppose Saturn at 25° 44' Sagittarius. But Saturn will be at 22°S00' declination, out of range of the contraparallel with Mars. So while the transit is exact in longitude, it is not in aspect by declination. The Mars-Saturn opposition is operative, but this Mars feels more like a wild horse, and Saturn like the would-be horse trainer.
With that, I'll say take care out there. And remember, if you get a wild hair later this month, the time could be just right to go for it - as long as it doesn't have the potential to harm yourself or others.