A sign in Arabic orthography always represent the sound of a glottal stop, transliterated in English as an apostrophe.
an indication (ء - a stand-alone hamza) used in the written Arabic language representing a glottal end. Hamza can take place as a stand-alone page or most frequently over or under other letters, e.g. أ (over an alif - ا), إ (under an alif), ؤ (over a wāw - و) or ئ (over a dotless yāʾ - ى). The actual seat of hamza is influenced by an orthographic rule - "chair of hamza guideline".