A few pointers from Csven to the discussion about SL residents using real-world trademarks:
-- Resident complains he (she?) was approached by a Linden employee and asked to remove cars modeled after Nissan and Toyota and sporting respective logos (SL Forums thread).
-- Linden Lab says any use of a real-life logo without permission is an IP infringement as is considered abuse under the terms of service (SL Forums post).
-- Clickable Culture: Second Life is rampant with intellectual-property infringements--it's just ignored (blog post).
The examples of residents using RL brands without (most likely) not having any legal right to do so abound and some of them are documented here. Some branded products (Coke from the vending machine) are given away for free, others (iPods at iPod store) are sold for money. There are two sides of the issue. On the one hand, these products and activities seem to be clear cases of IP infringement. On the other hand (as a recent C3 paper explains in detail), the companies abstain from twich reaction to every instance of illegal use / fan production as in some cases the benefit to the brand outweighs the cost of losing control.
Yet on the other (third?) hand, SL residents who market products under their own brand may view illegal exploitation of RL brand goodwill as unfair competition.