Я не понимаю подпись, которую вы мне показали.
I do not understand the signature which you showed me.
Breakdown of Я не понимаю подпись, которую вы мне показали.
не
not
я
I
вы
you (plural)
понимать
to understand
Questions & Answers about Я не понимаю подпись, которую вы мне показали.
Why is the word for 'which' written as которую here?
It refers back to подпись (signature), which is a feminine noun. It is in the Accusative case because it acts as the direct object in the second part of the sentence: the signature is the thing that 'you showed'. The feminine Accusative form of который is которую.
If подпись is the direct object of 'I do not understand', why doesn't its ending change for the Accusative case?
It actually is in the Accusative case! Feminine nouns that end in a soft sign (-ь), like подпись, belong to a special noun group. For these words, the Accusative form looks exactly the same as the dictionary (Nominative) form.
Why does the sentence use мне instead of меня?
Мне is the Dative case of я (I/me). We use the Dative case here because the verb показать (to show) requires it for the person receiving the action. You showed the signature 'to me'.
Is the comma before которую strictly necessary?
Yes! Unlike in English, where commas before 'which' or 'that' can sometimes be dropped, Russian grammar always requires a comma before a relative clause starting with a word like который (which/who).