This is not much of a “sign” but it is somewhat conncected to the topic, so I’ll mention it: If someone says this Sela I’m giving to Tzdakah so that my son lives or so that I get Olam Haba, he’s a Tzaddik Gammur (Pesachim 8a). Tosfos explains that as long as he won’t regret it if it doesn’t come to pass, this statement applies.
So sometimes you can “test” Hashem, but at the same time it might not come to pass.
The original question seems to be talking about something else though.