According to established case law of the boards of appeal, a mere investigation for indications of the presence of inventive step is no substitute for the technically skilled assessment of the invention vis-à-vis the state of the art pursuant to Art. 56 EPC. Where such indications are present, the overall picture of the state of the art and consideration of all significant factors may show that inventive step is involved but this need not necessarily always be the case (see T 24/81, OJ 1983, 133 and T 55/86). Secondary indicia of this kind are only of importance in cases of doubt, i.e. when objective evaluation of the prior art teachings has yet to provide a clear picture (T 645/94, T 284/96, T 71/98, T 323/99, T 877/99). Indicia are merely auxiliary considerations in the assessment of inventive step (T 1072/92, T 351/93).

In T 754/89 – "EPILADY" the board detailed its reasons for ruling that an inventive step was involved. Although factors such as commercial success, the overcoming of prejudice, the age of the documents cited, the cost of advertising and the creation of a new market segment, the satisfaction of a long-standing need, the existence of imitations and forms of infringement had received considerable attention, particularly in the parties' written submissions, the technical facts of the case were such that secondary indications of inventive step had lost any relevance.

In T 915/00 the board held that commercial implementation, licensing and the recognition of the inventor's merits by the scientific community constituted further convincing secondary indicia for the presence of inventive step.

In T 1892/12 the board observed that the boards had in some cases taken account of "secondary indicia" that an inventive step was involved but had not so far done so for the purposes of establishing that it was lacking. According to Art. 56 EPC, an invention shall be considered as involving an inventive step if, having regard to the state of the art, it is not obvious to a person skilled in the art. In view of the negative definition in Art. 56 EPC, the board considered that inventive step could never in fact be proven but that secondary indicia might sometimes show it was plausible. A lack of inventive step by contrast could actually be proven by conclusively showing that a solution was obvious. So proving a lack of inventive step was possible, in principle, and indeed necessary where such a lack was alleged; it was then not enough to point to secondary indicia.