This seems to be kind of a whole subject in itself related to Renaissance nobles and the ways they identified themselves. To try to make a long story short, "personal devices" or "heraldic emblems" (referred to in the asker's quoted text) or "badges" were a sort of less formal coat of arms used during the Renaissance. A certain style, in particular known as "impresa" in Italian, came to contain both images and some text in the form of a motto.

I think this is what your term is referring to, the text or "motto" included in these Italian-style heraldic emblems, which seem to be referred to most accurately by the Italian term of impresa (or imprese, the plural form, I think). The term I am suggesting specifies the text portion of the impresa.

For example, check out this page and scroll down to Figure 3 and the text quoted below, which seems to be a good concise explanation of this subject":

"The Personal Impresa

In the Renaissance, particularly in Renaissance Italy, a new type of insignia arose. Instead of being a very simple design, like the personal badge, this type of insignia was generally more complicated. It represented some philosophical ideal or allegory, and often had a scroll with a motto in it as part of the heraldic design.

These insignia are often known as “imprese” (the Italian term) or “emblems.” Imprese were often designed with a number of separate objects which suggests designing them with a background color for S.C.A. use. Despite their complexity, imprese were used for decoration and to mark objects, just like personal badges.

As an example, figure 3 shows an impresa from Renaissance Milan. It consists of a hand issuing from a radiant cloud, holding a bulging moneybag. The whole design is entwined by a motto scroll, which in Italian means either “when the time is right” or “when the weather is right.” This impresa refers to a philosophy on when to give money. The cloud plays on the “weather” meaning of the motto."
http://heraldry.sca.org/armory/whatis/badge.html

Also, this webpage contains lots of content on this subject as well, including this summary:
"In other words, an impresa is a combination of a picture (body) and motto (soul). It's used for individual self-expression, the picture should be fair, and the motto should be witty and in a foreign language.
The individual nature of an impresa is particularly important. One person might use many different imprese to express different ideas and moods, or to commemorate different occasions."
http://www.yarntheory.net/ursulageorges/imprese/imprese.html

You can see more on the subject at this wikipedia page in the Renaissance section, which includes:
"In the Renaissance, the badge, now more likely to be described as a "personal device", took an intellectual turn, and was usually combined with a short text or "motto", which when read in combination were intended to convey a sense of the aspirations or character of the bearer."
http://en.wikipedia.org/wiki/Heraldic_badge#The_Renaissance_...




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Note added at 2 hrs (2015-05-25 18:29:40 GMT)
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Although what I described above is I think the original source of the term, it is also possible that the asker's text is referring to later elaboration of these mottos into a form of poetry and/or song lyrics, which might be implied by the "como harían los emblemas heráldicos" in the past tense. So, depending on the larger context of the source text, the answer could also relate to something called villancico ( http://en.wikipedia.org/wiki/Villancico ).