There is no convention. You need to know how chords are notated. This is independent of what scale you may be operating in.
Chords have root notes, these notes are certain scale degrees on the scale. So the Tonic chord has the Tonic for a root.
Then comes details on what type of chord you have. The four main types you are going to need to know are.
Now let us go trough what these mean.
- Major - It has a Major Third and a Perfect Fifth
- minor - This has a minor third and a Perfect Fifth
- Diminished - Minor Third and Diminished Fifth
- Augmented - Major Third and Augmented Fifth
A major chord build on a certain scale degree will have it notated with a Capital Roman Numeral.
A minor chord will be notated with lower case Roman Numerals.
An augmented chord will be notated with Capital Roman Numerals and a plus sign to indicate that this chord has an augmented fifth.
A diminished chord will be notated with lower case Roman Numerals and the degree sign.
Then lastly you have the inversion. The inversion basically concerns itself with what notes is in the bass.
If the root note is on bottom it is notated with 5/3 or none.
If the third is on the bottom then it 6/3 or sometimes just 6.
And lastly if the fifth is on the bottom then 6/4
You need to be able to look at any chord regardless of key and be able to tell what type of chord it is. Many modern pieces only adhere to the key loosely so the tonic chord can be many types of chord.
It is only in standard western harmony that the type of chords follows a certain pattern.