This article investigates the claim that tongue protrusion (‘th’) acts as a nonmanual adverbial morpheme in British Sign Language (BSL) (Brennan 1992; Sutton-Spence & Woll 1999) drawing on narrative data produced by two deaf native signers as part of the European Cultural Heritage Online (ECHO) corpus. Data from ten BSL narratives have been analysed to observe the frequency and form of tongue protrusion. The results from this preliminary investigation indicate tongue protrusion occurs as part of the phonological formation of lexical signs (i.e., ‘echo phonology’, see Woll 2001), as well as a separate meaningful unit that co-occurs (sometimes as part of constructed action) with classifier constructions and lexical verb signs. In the latter cases, the results suggest ‘th’ sometimes appears to function as an adverbial morpheme in BSL, but with a greater variety of meanings than previously suggested in the BSL literature. One use of the adverbial appears similar to a nonmanual signal in American Sign Language described by Liddell (1980), although the form of the mouth gesture in our BSL data differs from what is reported in Liddell’s work. Thus, these findings suggest the mouth gesture ‘th’ in BSL has a broad range of functions. Some uses of tongue protrusion, however, remain difficult to categorise and further research with a larger dataset is needed.