In Steam Park, the danari values are only printed on one side, and the other sides are all the same. This suggests to me that a player's total should be kept hidden.
If it's intended to be an option, it's not documented.
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It looks like you have it correct.
The designer demonstrates hiding his income when explaining the prototype of the game in 2012. (T=8:23 of this video)
He says explicitly in this video from Spiel 2013: "Money are kept secret." (T=9:48)
Later video reviews and/or game play explainer videos also concur: