For purposes of truth in advertising, I'd think it's inappropriate to call your march a march "for science" if most of the marchers are really just marching against Trump. YMMV.
As someone who was at the DC march, and who was involved with March for Science, I can attest that while there were a very few signs which were specifically anti- Trump, those signs and those marchers comprised a very small number of marchers in DC. Judging from what friends who attended other marches told me, and photos shared from other marches, this held true across all US and international marches. Personally, I marched with people who work with various defense contractors and on occasion, with DoD.
Frankly, there was tremendous discussion about whether or not anyone should carry an overtly political sign at all. Most did not, but yes, some did. A few of these were anti-Trump, but more were specifically against denying science or funding for science. Those signs would have been carried no matter who was proposing the budget cuts, no matter who removed all mention of climate science from the EPA site, no matter who was proposing defunding medical research, the NIH, and so on. Trump be damned. And too fucking bad if his little minions cannot take the heat when people protest his policies.
Most of the discussion among marchers that I heard was that it was important to move away from directly criticizing Trump for trivial issues but to directly address the short and long term effects of his proposed budget and policies.
The vast, overwhelming number of signs and marchers were advocating for science, for the funding of science, for the importance of science. Some were specific to particular areas of science, some were more general. While many of the marchers were research scientists, there were also many, many doctors, nurses, laboratorians of various kinds, as well as science enthusiasts, etc. We were also supported by many in the arts community, some of whom are science enthusiasts, and some of whom support science and funding for science on general principal. And then, there were those who marched because their lives or the lives of their children or other loved ones depending upon scientific advances. Heartbreakingly, there were those who marched to support continued research because they had lost someone they loved to a disease which has no cure (yet).
Among those who participated in March for Science were those from all political persuasions, conservative as well as liberal. Marchers included a number of older people, many young people, and even small children and babies. And a few dogs, as well. Who presumably hold no political opinions at all.
I know this because I was there.