Add this code to your product template and it will only display on a specific collection. Courtesy of this Stack Overflow post.

{% for c in product.collections %}
{% if c.handle == "collection-handle" %}
Input custom text here. HTML is fine, as are other liquid modifiers.  
{% endif %}
{% endfor %}

Keep in mind that your “collection handle” might be different than your title, especially if you changed the title later (the handle remains the same). So for example, your collection name could be “Women's Dresses”, so your handle would most likely be “womens-dresses”. But if you later changed the collection title to “Women's & Girl's Dresses”, your handle may still be “womens-dresses”. You can find your handle by clicking “Edit SEO” on the Edit Collections page and seeing what comes after the .com/collections/_______.