das Markenzeichen
signature feature
A characteristic, typical feature of a person or thing by which they can be easily recognized.
Ihr roter Hut wurde schnell zu ihrem Markenzeichen.
Her red hat quickly became her signature feature.

trademark / signature feature
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signature feature
A characteristic, typical feature of a person or thing by which they can be easily recognized.
Ihr roter Hut wurde schnell zu ihrem Markenzeichen.
Her red hat quickly became her signature feature.

The word consists of 'die Marke' (brand) and 'das Zeichen' (sign). So it literally refers to a sign that represents a brand. The figurative meaning for a typical feature is also derived from this literal meaning.
Das Logo ist das bekannteste Markenzeichen des Unternehmens.
The logo is the company's best-known trademark.
You can recognize the figurative meaning by the fact that it is about a person and their personal, striking characteristics. The literal, legal meaning, by contrast, refers to companies, products, and protected symbols.
Seine laute Lache ist sein persönliches Markenzeichen.
His loud laugh is his personal signature feature.
When a feature is typical of a person, it is often described with the phrase `zum Markenzeichen werden` (to become a signature feature). It is something that has developed over time as characteristic.
Ihre bunten Kleider sind schnell zu ihrem Markenzeichen geworden.
Her colorful dresses quickly became her signature feature.
In the legal meaning, 'Markenzeichen' (trademark) is often combined with the adjectives `eingetragen` (registered) or `rechtlich geschützt` (legally protected). You can also `anmelden` (register) a trademark or `schützen lassen` (have it protected).
Die Firma hat ihren Namen als Markenzeichen schützen lassen.
The company had its name protected as a trademark.
brand / mark / stamp
'die Marke' and 'das Markenzeichen' can both have to do with a company's sign or name. 'Marke' usually means the product, the company, or the name under which something is sold. 'Markenzeichen' can be a legally protected sign, for example a logo. Very often, however, it also means a typical feature by which you recognize someone or something. Learners may confuse the words because they sound similar. For products, people usually say 'Marke'; for a recognizable special feature, 'Markenzeichen' is more likely.

Sein roter Hut ist inzwischen sein Markenzeichen.
His red hat has since become his signature feature.
Aylin achtet beim Kauf von Kaffee nicht auf die Marke.
When buying coffee, Aylin does not pay attention to the brand.