But there have been other suggestions.
A. M. Bell in his Visible Speech of 1867 describes the glottal "catch" (p. 60) like this:
The symbol he uses looks like the Greek letter χ or two round brackets (see comments below). In his list of consonant symbols on p. 93 we find a sample word written <buʼer>:
Here Bell indicates the glottal plosive by an apostrophe.
A. J. Ellis in the 4th volume of his Early English pronunciation of 1875 quotes Bell's example on p. 1344, but he uses the semicolon [;] for the glottal stop:
Bell is once again mentioned in Sweet's Handbook of phonetics of 1877 on p. xvi and p. 7. He calls the sound "glottal catch" and uses the symbol [x] for it:
In the 5th edition of his Grundzüge der Phonetik of 1901 Eduard Sievers states on p. 278 that the glottal stop ("Kehlkopfverschluss", which Sievers also calls "Stosston"), for which he uses the symbol [ʾ], replaces an oral closure in some English accents:
Daniel Jones in The Pronunciation of English (I have access to the 2nd ed. of 1914) uses the familiar glottal stop symbol (see p. xvi):
This blog posting is greatly indebted to Bjørn Ståhlhane Andrésen’s book Pre-glottalization in English Standard Pronunciation (Oslo, New York, 1968).