Much of this question depends upon interpretation and opinion. From a primarily textual and historical approach, we can discern thus...
In general, the 'moon turning to blood' can be considered a lunar eclipse. In particular, this being a portent of something is cited from the first chapter of the Bible.
Then God said, “Let there be lights in the expanse of the heavens to
separate the day from the night, and let them be for signs and for
seasons and for days and years;
As they were to be "signs", and to indicate "seasons", as well as for days and years, it is strong indication that they could mean something. Further, if one takes a "blood moon", Biblically, as a lunar eclipse, then the references to such indicate that some of the lunar eclipses have signified things.
If one looks at the crucifixion, assuming a date of April 3rd, 33 AD, we see from the Nasa Website that there was indeed a lunar eclipse on that day (see item 04904). Further, historian Plegon records the following:
In the 4th year of the 202nd Olympiad, there was a great eclipse of
the Sun, greater than had ever been known before, for at the sixth
hour the day was changed into night, and the stars were seen in the
heavens. An earthquake occurred in Bythinia and overthrew a great part
of the city of Nicæa.
[Plegon, "OLYMPIADES". In "Fragmenta Historicum Graecorum" (C. Muller) 1841-
1870, Volume 3, pages 603 - 624]
This darkness, recorded by a secular historian, however, was NOT a solar eclipse. As it was at the same time as the Lunar Eclipse previously mentioned, and a lunar and solar eclipse cannot happen at the same time (the moon must be on opposite sides of the earth with respect to the sun -- see here), this was an unexplained phenomenon. An interesting study of this can be found at The Bethelehem Star.
This puts sets the context for Peter's statement in Acts 2:20, quoting the prophet Joel,
The sun will be turned to darkness and the moon to blood before the
coming of the great and glorious day of the Lord.
Peter appears to be referencing these particular events from 50 days prior during Passover at the crucifixion. The sun was darkened as Christ died, and the moon rose in full blood red eclipse that night, beneath the constellation virgo, while Jesus lay bloody and dead beneath the "virgin", his mother.
Interesting to note, it is said (See Blood Red Lunar Eclipses for other thoughts) that the Jewish Rabbis are saying that the solar eclipse in the year 2015, in the midst of the tetrad, is to signify the year of the judgment upon the Gentile nations.
While it is true that certain Jewish feasts are always on the new moons, and that all lunar eclipses are always also on new moons, thus lessening the improbability of such an occurance, it is still the case that the number of tetrads documented in a Biblical history (6000 some years, assuming a young earth) is relatively limited (8 in the past 2,000 years - 8 blood moons ).
From this, from a purely analytical viewpoint, we can conclude.
- God set them up as signs.
- God prophesied them as signs.
- God uses them as signs.
- Most of the tetrads since the cross appear to be signs (to some).
- Not all signs are immediately, visible, globally effecting, or portent-ly significant, outside of a particular subset of the universe (not everyone felt the effect of it the moment it happened).
From this, it would appear it would be wise to be aware of such signs, although the particular interpretation of such events is one of faith.
The concordance says that the only references to a "blood moon" are Joel 3:21, Acts 2:20, and Revelation 6:12, however.
Is this tetrad important? Time will tell, won't it?
What is the Biblical prescription for discerning the times and being prepared? The same as it always is. Seek the Lord through Prayer (possibly with fasting), Biblical study, and a tender heart.
This is the only preparation, to be following Him, and to be listening to His Word, living a holy life, and dwelling in faith.