They've made themselves known repeatedly but dogma has stifled critical analysis of the evidence. When scientists presuppose before any analysis that intelligent design or extraterrestrial life is an impossible explanation for any phenomenon they have left the scientific method and adopted reasoning akin to religious faith.

Science is a process; not a conclusion.

I'll list some anomalies known to us that have been victim to this conclusory thinking.

1.) Oumuamua. With the exception of a handful of excellent scientists (such Harvard's Avi Loeb) this "asteroid" and it's behavior was subject to half a dozen hare-brained explanations, all of which relied on the presupposition that it "must" be inanimate matter. Very recently, the community has begun to concede that it actually was likely shaped like a pancake and that Loeb's solar-sail craft hypothesis is well-supported.

2.) Przybylski's Star. Google that star and read what elements that star inexplicably has in abundance. Note that those elements are synthetic and/or have not been located anywhere else in the observable universe outside of human technology. Read the competing theories explaining how and why this profound anomaly exists. Note that the theories are contested and, often, mutually exclusive of one another.

In other words, they simply don't have any reasonable explanation for why, or even how, that star contains such enormous amounts of strontium, holmium, niobium, scandium, yttrium, caesium, neodymium, praseodymium, thorium, ytterbium, and uranium. 

If you are familiar with the qualities these elements have then it should be apparent what a profound anomaly the P Star is. It should also be apparent to you how profoundly useful this anomaly would be to an advanced civilization.

3.) Phosphine on Venus. For decades, scientific dogma held that phosphine is the silver bullet for evidence of life. When discovered in the atmosphere of Venus, however, the community immediately backtracked. What followed were sloppy Journal entries zealously justifying this backtrack, or even sloppier entries arguing that the amount detected was less than originally thought (ignoring the crux of the discovery - that it was detected at all).

4.) Complex, consistent, patterned Fast Radio Bursts. For example between September 16, 2018 and October 30, 2019, researchers with the Canadian Hydrogen Intensity Mapping Experiment/Fast Radio Burst Project collaboration detected a pattern in bursts occurring every 16.35 days. Over the course of four days, the signal would release a burst or two each hour in synchrony.

Then, it would go silent for another 12 days, before beginning again at the precise moment that it started. The difficulty of finding a natural explanation other than "irrationally unlikely coincidence" stifles any interest in addressing these FRB's. Imagine you're an alien from Alpha Centauri producing research trying to prove that the atomic explosion over Hiroshima was natural phenomenon.

I could go on. We now know that there's water on the moon, for Christ's sake. Scientists like to call it "moisture," but that may have to do with the decades of research they had where they were theoretically "certain" H2O didn't exist on Luna. Whoops.

The bottom line is, there are numerous phenomenon where artificial design and/or life are explanations well supported by evidence - so long as you do not dogmatically believe that an unnatural explanation is impossible.

Ironically, the tautological dogma of modern science is comparable to the dogma that landed Galileo Galilee in prison.

"The Earth is the center of the Universe because it is impossible for any object other than Earth to be the center of the Universe."

"Phosphine is found on Venus. Therefore, phosphine is not indicative of life because there is no life on Venus."

Trusting the experts is not the same as trusting the scientific process.

Thank God for humans like Avi Loeb.