I'm thinking of men and women etc. that visit towns or town squares and yell about end of days, repent, Jesus will return and all that. Often they bear a cross or signage. It's definitely been a kind of thing for decades (perhaps centuries?), so I bet there's a word for it.
I want to say "town crier" but I know that's not right.
One term is street preacher, which apparently has been around since 1769:
street preacher n.
1769 B. Pye Five Lett. i. 10 Our prudent Leaders do not send out Field-Preachers, and Street-Preachers, to bawl down their Absurdities.— OED
A town crier is [or used to be] an official position for the publicising of borough notices, royal proclamations and the like.
@Andrew was quicker, so I will just post this in case it offers something supplementary.
Officially, without any connotation of irony, they are called street preachers. Wikipedia explains that:
Open-air preaching, street preaching, or public preaching is the act of evangelizing a religious faith in public places.
However, this endeavour has lost its popularity, attractiveness and efficiency due to factors which I will not go into in this post. This Christian site shows how the name of what was of old an honourable means to spread good, has slid towards negative connotations:
Street preaching, or preaching openly in a public area, has been a method used throughout the history of Christianity for the purpose of evangelizing people who would not typically enter a church. Ever since the apostle Peter preached in the streets of Jerusalem in Acts 2, Christians have used this method to lead many to faith in Christ.
Despite the long-standing tradition of street preaching throughout church history, some believe that the practice should no longer be used. Critics believe street preaching has lost effectiveness as compared to its results in past decades. Second, some believe that street preaching is too overt or offensive, that people are turned away rather than drawn to Christ. Third, some critics note that certain people have used the “soapbox” to spread extremism, political wrangling or bad theology, giving street preaching a negative association. As a result, they argue, Christians should use other forms of outreach. (gotquestions.org)
I have underlined the word soapbox, because it can be used ironically in connection with street preachers, although it is used for political speeches mainly, as those you would hear in London's Hyde Park Corner.
I know Urban Dictionary is not a favourite here, but I will risk it since it does address the meaning you describe:
Street preacher aka street prankster (alternative name)
They can often be found on street corners talking freaky stuff about the Lord and repentance and amusing, sometimes annoying, the general public.
Under the same entry you will find a reference about the Welsh music band Manic Street Preachers. :)
Much depends on the context - and you give none. On the one hand, we have
OED
God-botherer
n. depreciative (chiefly British, originally Military slang) a member of the clergy; any religious-minded person, esp. a proselytizing Christian.
and (chiefly US)
Holy Roller
n. colloquial a member of a religious group characterized by frenzied excitement or trances.
and on the other
Prophet
1.a. A divinely inspired interpreter, revealer, or teacher of the will or thought of God or of a god; a person who speaks, or is regarded as speaking, for or in the name of God or a god.
And between these there will be others.
Since your examples all deal with the end of the world in some way, my first thought was doomsayer. I always imagine a doomsayer as making their predictions as public outcries, but the dictionaries I checked don't include that part.
doomsayer (dictionary.com)
n. a person who predicts impending misfortune or disaster.
doomsayer (M-W)
n. one given to forebodings and predictions of impending calamity
In informal American English we have:
Bible-thumper
noun Informal.
an evangelist or other person who quotes the Bible frequently, especially as a means of exhortation or rebuke.
Source: Dictionary.com — bible-thumper
It can be found in use as early as 1810 — by a Scot:
. . . I do not believe that the boldest, and most new-modelled bible-thumper amongst the clergy of the present day, could have confounded and puzzled a piece of scripture better than I had contrived to do . . .
Source: The Spy, a periodical paper of literary amusement and instruction (1810)
What they're doing is proselytising (Cambridge), and the noun proselytiser (M-W, so "proselytizer") does exist, though it's not common.
In addition to the noun phrases street preacher and God-botherer/Bible-thumper, which I agree are applicable, I offer the adjective phrases fire and brimstone and turn or burn.
Dictionary.com, fire and brimstone:
threatening punishment in the hereafter: a fire-and-brimstone sermon.
I can’t find any dictionary entry for “turn or burn” (it keeps getting mixed up with unrelated military-derived slang “turn and burn”). In lieu of a citation, it was the title of a sermon by Charles Spurgeon; I can attest to its occasional usage in the Christian community; and I would tentatively guess that it could be understood by the general public even if they were unfamiliar with it.
These could be applied to the noun phrases to emphasise exactly what kind of preaching they’re doing (“a fire-and-brimstone street preacher”), or to more general terms (“the turn-or-burn crowd”).
