How are new forms of ‚socio-technical‘ sociality affecting the stability and dynamics of valuation in financial markets? For the past 15 years, research spearheaded by the Social Studies of Finance has struggled with this question. The evidence remains ambiguous: while the reliance on formal calculative procedures makes valuation more reflexive, paradoxically this reflexivity can both serve as a corrective to self-recursive valuation dynamics, and feed into them as a catalyst at other times. In this paper, I develop a relational-semiotic account of financial valuation and markets which allows us to examine under what conditions calculative devices enable stable forms of social coordination. Conversely, I show that when the abstractions which underpin such devices are incommensurable with the substantive (informal) category systems through which relational ‚value‘ is encoded, formal calculation will become pathological. Using the financial arbitrage conducted through the Black-Scholes-Merton formula as an illustration, I show how a semiotic analysis can elucidate when, how and why formality fails in financial markets.