Apart from the ordinary letters of the alphabet, we propose the special symbols · and ’. The symbol · denotes that a word has an acute accent rather than an expected grave accent, and ’ denotes that a word has a grave accent rather than an expected acute accent. With "expected" we mean how the word's pronounciation would have been a priori perceived if the special symbols weren't present to specify the correct accent.
Historically, · means that we have an Old Norse compound of a monosyllabic word (noun, pronoun or adjective) and a suffixed definite article. Such words have an acute accent today, while other bi- (or multi-) syllabic words have a grave accent. As a concrete example, take ON hús 'house', which by adding the definite article it 'the' becomes húsit 'the house' in the definite form. Of course, we could use a more morphologically etymological spelling hús·it to account for the fact that -it has been added. The reason we use · here is that it's a common way of writing a shorthand hyphen. A spelling hús·it would definitely have made sense to the speaker of Old Norse since the difference between acute and grave accents existed also back then. Thus, we'll write hús·eð [hʉːsə] (acute accent) in Jamtlandic. Had we written "húseð" it'd meant [hʉːsə] (grave accent). Note though that due to the fact that we orthographically respect syncopation in words with acute accent, we don't need the shorthand hyphen in a word like hestn [hɛstn̩] (acute accent) 'the horse', from ON acc. hest·inn, i.e., hest + inn. (Modern Jamtlandic indefinite form hest [hɛst] 'horse'.) We also don't write out the shorthand hyphen when the word has a grave accent, though being a compound with a suffixed definite article. For example, hestan [hɛstɐn] (grave accent) 'the horses', from ON acc. hesta·na, i.e., hesta + ina. (Modern Jamtlandic indefinite form heste [hɛ.ɛst] (grave accent) 'horses'.)
The etymology for ’ is due to the syncopation of a vowel in a word with a grave accent. The reason we use an apostrophe is of course due to the fact that it by tradition denotes a dropped letter. As an example, take ON lítinn (a variety of ON lítill) 'little' which in Jamtlandic has become [liːtn̩] (grave accent) with a syncopation. Following the recipe, we write this lít’n, where ’ accounts for the syncopated i indirectly preserved in the grave accent.
The alt codes for the special symbols above are
alt+250 to produce · (hyphen), and
alt+0146 to produce ’ (apostrophe).
Of course, if a Jamtlandic keyboard is ever produced, these would be easily accessible. (One can use a Swedish physical keyboard to create one's own Jamtlandic keyboard layout. This isn't important at this early stage, but it's important to mention the possibility of customizing the keyboard layout such that the alphabet and special symbols of Jamtlandic can be accessible without employing the somewhat tedious alt codes.)