The following examples will help you to check if a product belongs to a custom collection or they have a certain tag:
{% assign in_coming_soon_collection = false %}
{% for collection in product.collections %}
{% if in_coming_soon_collection == false and collection.title == 'Coming Soon' %}
{% assign in_coming_soon_collection = true %}
{% endif %}
{% endfor %}
Checking if product has a tag. Mind that tags are case sensitive and spacing matters.
{% for tag in product.tags %}
{% if tag contains 'silk' %}
{{ tag }}
{% endif %}
{% endfor %}
From: https://stackoverflow.com/questions/41966028/shopify-liquid-if-product-has-a-tag-echo-that-tag
