Linguists have a whole mess of symbols that they use, but it’s difficult to find a full list of them anywhere, so I started compiling one here. If I’m missing something, please let me know in the comments.
A very common symbol to start with is the * symbol. It means “this is not a grammatical sentence”. This is strictly used to mark grammaticality like in (1) and (2), and it’s not used for sentences which are just badly written (3) or which are nonsensical (4).
(1) *Who is this the book which you gave to?
(2) *Some people ever meet the Prime Minister.
(3) Having finished the housework, the TV was turned on.
(4) The bacteria coughed.
If a star appears with a bracket, then there are two ways to interpret
it: writing (*word) means that the sentence is ungrammatical if you
include the word, and *(word) means that the sentence is ungrammatical
if you exclude the word.
(3) I laughed (*it)
(4) I devoured *(it)
Another common symbol is ? which means the sentence sounds wrong, but
you’re not sure if it’s full-on ungrammatical:
(4) ? What does Fred wonder where Jill went to purchase it
These are sometimes also combined, especially to indicate that one
sentences “not quite” ungrammatical:
(5) ?* Fred wonders what did Jill buy
Allegedly there are differences between *? and ?* but I honestly think
that makes too fine a distinction for it to be of any use.
A somewhat more rare symbol is the % sign, which is used to indicate
that this is grammatical for a percentage of the population, but it’s
not widespread. I’ve never personally used this, but I think it would
be OK to write:
(6) %He drinks cream in his coffee anymore.
The # symbol is used to indicate that something is pragmatically or
semantically weird, but not necessarily ungrammatical:
(7) i. Alice: They hired that bastard Derrick!
ii. Bob: That’s not true, they hired Louis! (fine)
iii. Bob: #That’s not true, you like Derrick. (odd)
(8) #It must be raining.
(when uttered while standing in the rain)
The most common symbols in phonology that people have trouble with are / / and [ ].
Words that appear in slashes, like /kip/ (which is “keep” in IPA transcription), are underlying representations, or underlying forms. Underlying forms are words before any phonological changes apply. If something can be derived by rule, then you should go derive it somewhere else, and you should not include it in the underlying form.
Words that appear in brackets, like [khip], are surface representations, or surface forms. This represents words after phonological changes have taken place. In this case, I chose to represent the aspiration on the [kh] in the surface form, but not in the underlying form /k/. This is because aspiration predictably occurs in syllable-initial position. There are other details that might be transcribed as well. How much information goes in really depends on the needs of the linguist and the audience, and there are no particular rules for this.
The symbol . is generally used to mark syllable breaks in a transcription, e.g. “magazine” [mæ.gə.zin]
The * symbol is used in phonology to indicate a word that doesn’t obey the phonotactics, in much the same way it is used in syntax to show a sentence is ungrammatical. For example in English, *bnick, *thrikm, or *tptik could be starred.
In historical phonology the * symbol is used to mean “unattested”, i.e. we have no direct evidence that this is a possible form of a language. For instance, the first person plural in Proto-Indo-European may be written *wei to indicate it’s a re-constructed (not directly attested) form. In a sense, this is still what it means, since if word is phonotactically ill-formed (or a sentence is ungrammatical) then is should be unattested as well.
The symbol # is used in phonology to represent a word boundary, which is completely different from its use in syntax.
The capital letters C, V, and N are frequently used as shorthand for ‘consonant’, ‘vowel’, and ‘nasal consonant’. This is especially the case when describing phonotactic rules, e.g. “this language has CVC syllables”
The underscore symbol _ is used in phonology to indicate a particular environment in a word. Other symbols can appear to the right and left to indicate the specifics of the environment. For example, you can write V_V to refer to an environment between vowels, and _# means “word-final”.
A hyphen – is used to indicate morpheme boundaries generally. The word unrefundable would be parsed out as un-re-fund-able. The equal sign = is often used to indicate clitic boundaries specifically.