I have the effect you are talking about, but am at work right now. I will see what it was when I get home tonight. (I think Capt Nemo might be right though, that it is the SH4 effects for SH3..but I am not absolutely sure)
I just attacked a convoy a day or 2 ago, and there were starshells from the merchants as well as a red distress flare from the one I sent down. (also, several merchants had their search lights on as well....it was quite the light show!)
Dale