Urban inscriptions are performative devices that play a crucial part in urban assemblages. They mark sites, give places a name, designate directions. This paper questions such performativity by investigating the design and maintenance of subway signs in Paris. Studying backstage activities rather than user tactics, it shows that the semiotic production of space is mainly played out in standardization processes that are both oriented towards signs immutability and fueled by a daily consideration for their vulnerability. Such a posture allows us to take full account of the ontological variations of signs (which can be, for example, stable or unstable, consistent or fragile, immutable or mutable). Maintenance work, through which the agency of urban inscriptions is partially shaped, ensures the articulation of such a multiplicity.