The small っ (tsu) is usually used before a consonant to indicate gemination, less technically known as doubled consonants, which is how they are transliterated in romaji.
I have seen it at the end of some of what I call "vocal noises" where I interpreted it as possibly a glottal stop. But the other day I saw it used on an advertising poster on public transport at the end of a word. At least so it looked. What does it signify in this case?
The text in the ad is:
お待たせっ!
新しいタフマン
参上!!
It's a glottal stop, similar to the usage you mentioned (あっ, もうっ). It signifies that the last mora is cut off abruptly. This can imply irritation (なんだよっ "What!") or excitement (大変だっ "It's terrible!"). In print, it's a little like adding an exclamation point to the end of the sentence.
I'm Japanese native speaker.
In my opinion, little "っ" at the end of sentence is not pronounced at all.
However, it often indicates "small" (not so serious) emotions of speaker, I'll show you some example, comparing with other two expressions for writing:
01. ふざけんなよっ
02. ふざけんなよ…
03. ふざけるなよ！
(All sentences mean "Don't be silly")
As you see, first sentence is the case including "っ" at the end.
On this case, I feel speaker doesn't get angry so much.
Let's imagine the scene in which friends are talking, and some person says a joke. If I express his friend's reply to writing, I will use above first expression.
On second one, I feel speaker tries to inhibit his/her emotion (but it often fail, because emotion is too intense). Here is good example.
This is really famous scene of Dragon Ball. Freeza killed Kuririn, which enraged Goku.
Firstly Goku speaks so calmly, but in fact he has strong emotion inside.
After that, he can't inhibit his emotion, and he will be next form? I read it long time ago, so I'm not sure.
Anyway, "―――!!!!!" and little "っ" are used in below scene. Watching these expressions, We can recognize his voice is sustaining with anger.
You might feel it's strange to use little "っ" now. In my opinion, this give us a kind of "light" nuance. The author might not have used it if he had written his story to strict novel.
In conclusion, by using some signs or something like little "っ" at the end, we can express speaker's emotion in writing.
Your example case is a little strange and without more context, I am not sure about the intent.
In general cases, just like Amanda said: it indicates a word being cut-off (or sometimes a very strong exclamation).
An interesting aspect is that it seems to work a little different from the equivalent in Western languages, in that it does not actually cut-off the word (in the text), but is added at the end. Let me illustrate...
If a comic book character was trying to say something, to be cut off suddenly (by another character, by a sudden event), the English would read something like:
What's happen... [cut to horrible monster devouring the hero]
the end of 'happen[ing]' being removed, is what indicates the abruptness of the cut.
The Japanese version would more likely be:
なんだっ！？ or なにこれっ？！
Both of which would be fully-formed words without the っ.
So, っ at the end of a word means something like "imagine the last mora of this word wasn't uttered", rather than "the rest of this word was cut-off", as a Westerner could be inclined to see it.
From what I've experienced due to learning Cantonese and Mandarin, the Tsu is used often as a way to create a short abrupt stop on the previous character but also to raise the tone of the character too? As we have tones in Cantonese in a similar way, I noticed that there is always a higher pitch to the shorter more abrupt form of the word. I guess it's used sometimes as a way to present surprise or raised pitch and in the case of the DragonBall Z image above, it's probably to present the slow rising of the last KAAAAAAA! if anyone knows DragonBall, the explosive energy of their shouts always rise up or the ka me ha me HA! is always raised higher in tone.
That's my beginners interpretation of the use of this character.
