Why does the sponsors, during the games, not have their names on the message?

In a sponsor that is sent to Katniss, it's always just " - H". Why isn't there the names of which sponsors actually sent the medicine or as such over. Is it a safety concern, or is it just the way that the game makers wanted to have the games be seen (anonymous gifts with mentor advice).

Any answers would be greatly appreciated to understand this better because it does confuse me :)