TL:DR; I support the proposal to have warning for some words in titles. But I do not think it would be good to blacklist them completely.
It is explicitly pointed out in How to write a good MathOverflow question? (the section "Make your title your question") that it is good to make the title describe the question as well as possible. And there indeed are several words which might indicate that the title is very likely rather vague or subjective. There are also words which typically work in a title as unnecessary filler.
I agree that it would be good to have a warning shown to a poster when the title contains some of these words. But I don't think it would be good to outright ban some words in the titles.
I think a solution similar to the one currently used on Mathematics site might be reasonable. See here: Should the site have an automatic word filter for titles? and Which are blacklisted tags and blacklisted phrases?. (The first link is the discussion which lead to introducing this. In both posts you can also see a complete list of words that trigger this warning. This list seems quite reasonable to me.)
The word urgent is currently not in this list on Mathematics, although there is a feature request to add it: The word “urgent” in a title should trigger a warning.
I should add that I do not know whether a similar filter is currently setup on MathOverflow. Probably SE staff and moderators have access to list of blocked words. But at least I can tell that some time ago a moderator (François G. Dorais) confirmed in chat that there is some blacklisted stuff also on this site
we hardly ever blacklist tags. We do blacklist other things but not tags. "completeness" and "untagged" are the only two.