Quote Originally Posted by BappaBa
Quote Originally Posted by Basil77
Я тут сомневаюсь. Обручальное кольцо - wedding ring. Engagement - это только помолвка, а ещё не wedding.
Ты думаешь у них для помолвки одно кольцо, а для свадьбы другое?
Yes, wedding ring and engagement ring are two different rings.
We don't have a short set name for engagemnet ring, because this tradition is just beginning to get restored. You coukd say "кольцо для помолвки", but it's too long and doesn't sound good.

I think that Basil77's variant (in blue) is perfect. It says "This is a ring for my girlfriend, I'm going to propose to her", which sounds very natural in Russian. You might add "Пожалуйста, не испортьте сюрприз" (Please don't ruin the surprise) or "Пожалуйста, не выдавайте меня" (Please do not give me away).