BGN/PCGN romanization (1981) uses a right single quotation mark (more accurately, a modifier letter apostrophe) to express aspirates, tʼ, chʼ, tsʼ, pʼ, kʼ, the opposite of the original rough breathing diacritic.
This system is recommended for international bibliographic text interchange (it is also the base of simplified romanizations found to localize the Armenian toponomy of for transliterating human names), where it works very well with the common ISO/IEC 8859-2 Latin encoding used in Central Europe.
Note that the input methods recognize the Latin digraphs zh, dz, gh, tw, sh, vo, ch, rr for Classic or Eastern Armenian, and zh, dz, tz, gh, vo, ch, rr for Western Armenian, but offer no way to disambiguate words where the digraphs should not be recognized.
However, cells with red background contain transliterations that are context dependent (and may in some cases create ambiguities, only the ISO 9985 and Hübschmann-Meillet romanizations do not use any context-dependant ambiguous digraphs for transcribing simple Armenian letters that are not ligatures, but the former is inconsistent with its representation of aspirated consonants and incompatible with all other systems for a pair of letters).
However the last column displays the ligature that is used in the Classical orthography only as an isolated symbol for the short Armenian word ew (meaning and) and its derivations in a way similar to the ampersand (&) in the Latin script (in the Reformed orthography, it is also used at the middle and the end of words instead of եվ); the same transliteration to ew (classical Armenian) or ev (reformed orthography) will be used for the letters this ligature represents, when they are used as digraphs: it used to refer to the w consonant, now it refers to the v consonant.
Armenian script also uses some other digraphs that are often written as optional ligatures, in lowercase only (five of them are encoded in Unicode only for full roundtrip compatibility with some legacy encodings); when present, these ligatures (which are purely typographic and carry no semantic distinction in normal Armenian texts) must be romanized by decomposing their component letters.