An application of Peircean semiotics to posters that were mandating the wearing of masks during the Covid-19 pandemic shows that iconic representations, in this case pictograms, are effective in conveying a message, especially within a specific social context, i.e. when the deciphering of the sign is facilitated by collateral information, and when the message becomes pervasive. On the other hand, when a receiver does not cognize a particular environment, and when the message becomes more subtle than a simple command or prohibition - like a recommendation or invitation, for example - it becomes vital to complement iconic communication with symbolic items in the form of text, provided that the code is accessible. Images are often immediately comprehensible as signs, but this does not necessarily mean that the message itself is understood and that the semiotic act ends in success.