Yes ,it is actually not a German word not even a loan word from another language. I found it in several articles though and found out that they mean stickers or buttons or even a piece of paper with short messages , opinions or statements.

First I thought of a button you have to press in order to give a test vote. To express your opinion. (In two weeks we have federal elections in Germany.) Zuerst habe ich an einen Knopf gedacht, den man drücken muss, um eine Test-Wahlstimme abzugeben. Um deine Meinung auszudrücken. (Wir haben in zwei Wochen Bundestagswahl in Deuschland. Then I tried to find out more about it. It's new to me. Seems to be a crude translation of "button". It is a sticker you wear on your clothes. To show your emotion or to express your opinion. We usually call it "Button" in German, too. Dann wollte ich mehr darüber herausfinden. Es war mir neu. Scheint eine grobe Übersetzung von "Button" zu sein. Das ist ein Anstecker (/eine Anstecknadel /ein Button), den man an der Kleidung trägt. Um seine Gefühle oder seine Meinung auszudrücken. Wir nennen das normalerweise in Deutsch auch "Button".

I am German, but I have really never heard that word :-) Not even my German dictionary knows this word. I can only imagine a context in which you shall vote for something. To give your vote/your opinion you have to press a button "yes or no" for example and that's what they are calling the "Meinungsknopf".

Hello Radwa, "Meinung" means rather " opinion, estimation or judgment " but not "idea". "Knopf" has another meaning beside " button " ,it could mean " a small piece , knob or pommel". The word "Meinungsknopf" means a small piece of paper or any material with an opinion written on it that is demonstrated in different events".