Sign languages, like creoles, have been minoritised in linguistics. This makes perspectives on creoles the potential to illuminate the study of sign languages. A common way that sign languages are divided is into deaf and rural groups, based on social criteria. This distinction makes relationships between social and linguistic properties relevant. This paper investigates one such causal relationship, specifically whether extent of contact with spoken language(s) via institutionalised education translates into higher prevalence of the silent articulation of spoken words, mouthing. Across 37 sign languages (26 deaf; 11 rural) mouthing is prevalent regardless of language type, having been reported in 35 languages (25 deaf; 10 rural). This suggests that differences in language emergence do not produce a structural difference in terms of mouthing. Language documentation should include description of contact phenomena and ideologies, and comparison can avoid stereotyping of language groups based on tokenised cases (de facto prototypes).